Nav: Renaming NavInitDefaultRequest -> NavInitRequest

Nav: Moving code next to its peers

Nav: Caching into g.NavAnyRequest to minimize hot path cost (and so we can add many more request sources)

Nav: Minor tweaks in NavProcessItem() used by ItemAdd()

Nav: Minor tweaks also toward removing processing from ItemAdd()

Internal: ItemAdd() minor shallow tweaks

Merge branch 'master' into navigation ...

# Conflicts:
#	imgui.cpp
#	imgui_internal.h

Internal: ItemAdd(), IsClippedEx(): removed unnecessary indirection for ID parameter

Removed extraneous calls to GetCurrentWindowRead() when we already have a ImGuiContext. Internal RenderXXX functions also don't need to write into the Accessed field at all.

Merge branch 'master' into navigation

Comments (clarifying whether types are to be considered as flags or regular, non combinable enums)

Nav: Shuffled code in ItemAdd() so that NavProcessItem() may have access to LastItemId (will be required by tabbing)

Nav: Minor midying up and comments,

Nav: Removed possibly redundant test prior to calling NavProcessItem() from ItemAdd()

Nav: Moving code next to its peers

Nav: Moving the big chunk of code from ItemAdd() to NavProcessItem()

Added ActivateItem(), GetItemID() functions.

Nav: Tidying up activation mechanism so that setting NavActivateId can trigger buttons.

Nav: Fixed uninitialized context variables for sanity.

Demo: better demo for SetKeyboardFocusHere()

ColorButton: Reduced bordering artefact that would be particularly visible with opaque Col_FrameBg and FrameRounding enabled.

Nav: Fixed uninitialized context variables for sanity.

TextUnformatted(): minor tweak

Made AlignFirstTextHeightToWidgets() saner and faster (still disliking its name very much!)

Merge branch 'master' into navigation

Nav: Menus and popups now have move request wrap around vertically (using the move request forward thing added recently). (#787)

SetKeyboardFocusHere() added assert to prevent passing values smaller than -1 as we may have to outlaw them (I think nobody was using that)

Removed obsolete comment.

Examples: Adding Roboto to the commented-out font list, and removing the unnecessary ProggyClean from there.

Merge branch 'master' into navigation