Nav: Minor tidying up. (#787)

Merging the minor/shallow changes from Navigation branch.

Added assert in BeginChild(ImGuiId id).

Nav: Debugging stuff.

Nav: Ensure g.NavScoringRectScreen is always finite and not inverted. (#787)

Merge branch 'master' into navigation ...

# Conflicts:
#	imgui.cpp

Style Added style.MouseCursorScale, may remove (#939).

Nav: Press Left on a child with ImGuiTreeNodeFlags_NavCloseFromChild moves you to parent node instead of closing it immediately. More standard. (#787, #1079)

Nav: TreeNode: Added ImGuiTreeNodeFlags_NavCloseFromChild flag, allow closing a TreeNode() from any of child. The explicit flag is not great, perhaps allowing some form of inheritance would help. (#787, #1079)

Nav: Revert 5c9ea4d with comments. (#787)

Nav: Modal windows can't be closed with Nav PadCancel. (#787)

Nav: Comments (#787)

CloseButton: Fixed cross positioning.

CloseButton: Fixed cross positioning.

Nav: When focusing a parent window while closing a popup, hide its highlight for one frame to avoid potential double highlight and flicker with the common pattern of menu items leading to the opening other windows. (#787)

Nav: Fixed Selectable/MenuItem Nav Highlight from using rounding when outer highlight stays square. (#787)

Nav: CloseButton reacts when clipped. (#787)

Nav: Fixed press Left on sub-menu when parent wasn't a menu - we were just checking at the wrong level. (#787)

Nav: Child window is restored on focus follow up. Fix bdd8687. (#787, ~#727) One visible issue was pressing Left to leave a child menu.

Metrics: Displaying some of the important internal window flags.

Merge branch 'master' into navigation

Internals: Renamed CloseInactivePopups() to a better ClosePopupsOverWindow(). Exposed in imgui_internal.h

Nav: Using CTRL+TAB / PadFocusNext/Prev to Focus a window closes the previous window popups. (#787)

Nav: SetFocusID() clears NavInitRequest for consistency (repro would a same frame interaction / race condition). (#787)

Nav: Fixed InitRequest leaking when changing window (repro was to navigate inside File->Options->[Child] then press Left and notice how we would land on parent window on the fist item after the current one). (#787)

Internals: Nav: Extracted code into IsWindowNavFocusable(). (#787)

Nav: Child window is restored on focus when returning to layer 0 or refocusing. This is a little experimental and potentially error-prone right now. (#787, vaguely relate to ~#727) Ideally we should maintain a non-sorted last-focused list that include childs windows.

Nav / Slider: Fixed reaching edge of integer slider with navigation input, bug introduced on January 25 in Nav branch 10a4a77. (#787)

Merge branch 'master' into navigation ...

# Conflicts:
#	imgui_demo.cpp

Internal: Avoid needlessly bringing parent of front-most child back to front. This is mostly to reduce flicker/confusion in Metrics when traversing windows. We could aim at separating the child windows from non-child windows at some point.