Merge branch 'master' into docking ...

# Conflicts:
#	imgui.cpp
#	imgui.h

Selectable: add support for specifying text alignment on selectables (#2347) ...

Adds a style variable to Selectable that allows clients to specify the
text alignment within Selectables, adds a section in the demo to
demonstrate selectable text alignment, and a pair of sliders in the
style editor to change selectable alignment on the fly.

In terms of implementation, this one is extremely simple: Selectable was
already calling an API that supports text alignment, but had hard-coded
it to top-left. This changes that to just pass the style variable
straight through to RenderTextClipped. Backwards-compatibility is
preserved by defaulting the text_align parameter to (0, 0), i.e.,
top-left.

This also fixes a bug with selectable text rendering that caused
right-aligned text in a selectable to be clipped incorrectly, because
the wrong clipping rectangle was being used.

Scrollbar: Fade out and disable interaction when too small, in order to facilitate using the resize grab on very small window, as well as reducing visual noise/overlap. (+1 squashed commits) ...

Internals: Added GetScrollbarID(). (#1185)

Shallow tweaks

Merge branch 'master' into docking ...

# Conflicts:
#	examples/imgui_impl_opengl2.cpp
#	examples/imgui_impl_opengl3.cpp
#	imgui.cpp
#	imgui_widgets.cpp

Tabs: Fixed border (when enabled) so it is aligned correctly mid-pixel and appears as bright as other borders.

Merge branch 'master' into docking ...

# Conflicts:
#	imgui.cpp
#	imgui_demo.cpp

ListBox/InputTextMultiline: Better optimized when clipped / non-visible.

DragScalarN, SliderScalarN, InputScalarN: Removed unnecessary string id after the integer PushID() calls.

Minor tweaks to reduce false positive of PVS Studio static analyzer.

Menus: Tweaked horizontal overlap between parent and child menu (to help convey relative depth) from using style.ItemSpacing.x to style.ItemInnerSpacing.x, the later being expected to be smaller. (#1086)

Plot: Register an ID to take the click the same way as other framed widgets. Set HoveredId in the FramePadding zone (between inner_bb and frame_bb).

Internals: Selectable: Fixed rendering width miscalculation when starting pos is not line start pos, which would generally be unnoticeable. Could affect group lock X with a smaller SetCursorPos value but that's unlikely to be used.

Internals: Removed unnecessary code.

Merge branch 'master' into docking ...

# Conflicts:
#	imgui_internal.h
#	imgui_widgets.cpp

Tabs: Moved Tab List Popup to left-side to match docking button. Highlight selected tab. (#261, #351)

Tabs: Non-docking tab bars are storing names to allow tab list button + whole style scaling. Added ImGuiTabBarFlags_TabListPopupButton flag to show a popup button on manual tab bars. Locking FramePadding for the scope of a tab-bar to avoid sheering/clipping of tab item. Made scaling of tab ellipsis less awkward. (#261, #351)

RadioButton: Fixed label horizontal alignment to precisely match Checkbox(). + Internals: Checkbox, RadioButton: Single call to ItemSize() for flow layout purpose.

Internals: DragScalar, SliderScalar: Calling ItemSize before ItemAdd as with every other widgets so we can more easily rearrange the signature of ItemXXX functions (toward allowing non-rounded sizes for scaling and flow layout).

Merge branch 'master' into docking (enable range_select merge) ...

# Conflicts:
#	imgui.cpp
#	imgui_internal.h

Internals: Minor changes to TreeNodeBehavior() and Selectable() for the benefit of fhe range_select branch. (#1861)

Internals: Track ActiveIdHasBeenPressed (similar to ActiveIdHasBeenEdited). This is currently mostly for the benefit of the range_select branch. (#1861)

Merge branch 'master' into docking ...

# Conflicts:
#	imgui.cpp

Docking: VisibleWindow of a node spread its _NoMove attribute to the node (fixed dragging or undocking of dock node host from collapse button). (#2325, #2109)

Docking: Fixed faulty undocking of windows with the _NoMove flag. (#2325, #2109) ...

Whereas BeginAsDockableDragDropTarget could be reworked to filter, we simply set g.HoveredWindowUnderMovingWindow to be NULL when MovingWindow is not set, which was the initial intent.
Also fixed some comments and removed unused braces in TabItemEx().

Docking: Removed unnecessary ImGuiTabItemFlags_DockedWindow internal flag.

Internals: InputScalarAsWidgetReplacement: Fixed seemingly unnecessary calling of SetActiveID/SetHoveredID every frame, which in turns allow us to remove the g.ActiveIdAllow/Block settings duplicated.

InputText: Fixed a bug where ESCAPE would be first captured by the Keyboard Navigation code. (#2321, #787)

InputText: Fixed a bug where ESCAPE would not restore the initial value in all situations. (#2321) [@relick]

imgui-test: Added extra item info callbacks. Using nav_bb for interactions when possible. Comments, Demo tweaks.