Merge branch 'viewport' into docking ...

# Conflicts:
#	imgui.cpp
#	imgui.h
#	imgui_internal.h

Viewport: Added ImGuiWindowClass / SetNextWindowClass() (concept imported from Docking ImGuiDockFamily), which currently allows to overwrite viewport flags on a per-window basis. Exposed FindViewportByID(). Win32: Support for ParentViewportId. (#1542)

Viewport: Win32: Workaround to the fact that ::WindowFromPoint() seems to return Windows using ImGuiViewportFlags_NoInputs / HTTRANSPARENT when dragging nearby the platform title bar. This is to allow using platform decoration. I don't understand this well atm. (#1542)

Viewport: Added Platform_UpdateWindow hook for general purpose: Rework Win32 code to reflect viewport flags changes into Win32 while the window is active.

Merge branch 'master' into viewport ...

# Conflicts:
#	examples/imgui_impl_sdl.cpp

Examples: Comments about GLFW/SDL versions

Tweaked asserts

Viewport: Misc comments following user feedbacks..

Fix merge in Docking branch, remove ConfigDockingWithShift flag from DX11 example + misnamed function.

Merge branch 'viewport' into docking

Build fix for master.

Merge branch 'master' into viewport ...

# Conflicts:
#	examples/imgui_impl_sdl.cpp

Examples: SDL: Avoid testing for SDL_GetKeyboardFocus() on Android and iOS (like Emscripten). (#421)

Examples: SDL: Fixed compilation for SDL 2..0.3 and less (running on our test servers) and clarified a bit of the messy situation. Followup to 8dd83c5. (#1542, #2117)

Merge branch 'viewport' into docking ...

# Conflicts:
#	examples/example_allegro5/main.cpp
#	examples/example_win32_directx9/main.cpp

Merge branch 'master' into viewport + added style tweak block when viewports are enabled ...

# Conflicts:
#	examples/example_glfw_opengl3/main.cpp
#	examples/example_sdl_opengl3/main.cpp
#	examples/example_win32_directx11/main.cpp

Examples: Setting up style before bindings, so in complex binding (vulkan/dx12) it isn't miles away from the context creation.

Examples: Viewport: Moved the "make current GL context" to reduce the amount of call and hopefully be more explicit about viewport enabled vs disabled requirements. (#1542)

Examples: SDL: SDL_GetMouseState() seems problematic, movements feels laggy in the non-viewport code path. (#1542, #2117)

Merge branch 'viewport' into docking

Viewport, DPI: Now using DpiScale from the ImGuiPlatformMonitor array instead of calling Platform_GetWindowDpiScale() before the platform window creation. Might even tentatively see if things work out without Platform_GetWindowDpiScale. (#1676)

Merge branch 'viewport' into docking + moved io.ConfigFlags ImGuiConfigFlags_DockingNoSplit to io.ConfigDockingNoSplit ...

# Conflicts:
#	imgui.cpp
#	imgui.h
#	imgui_demo.cpp

Merge branch 'viewport' into docking ...

# Conflicts:
#	imgui.cpp

Viewport: Win32, GLFW, SDL: Clarified back-ends by using global mouse position direction. GLFW: disabled io.MouseHoveredViewport setting under Mac/Linux. (#1542, #2117) + various comments.

Merge branch 'viewport' into docking ...

# Conflicts:
#	docs/CHANGELOG.txt
#	imgui.cpp

Merge branch 'master' into viewport ...

# Conflicts:
#	examples/imgui_impl_dx10.cpp
#	examples/imgui_impl_dx11.cpp

Examples: DirectX10/11/12: Made imgui_impl_dx10/dx11/dx12.cpp link d3dcompiler.lib from the .cpp file to ease integration.

Merge branch 'viewport' into docking ...

# Conflicts:
#	docs/CHANGELOG.txt

Somehow VS keeps modifying this GUID so I am going to playing along with it.

Merge branch 'master' into viewport ...

# Conflicts:
#	docs/CHANGELOG.txt
#	examples/imgui_impl_dx10.cpp
#	examples/imgui_impl_dx11.cpp
#	examples/imgui_impl_dx12.cpp
#	examples/imgui_impl_glfw.cpp
#	examples/imgui_impl_opengl2.cpp
#	examples/imgui_impl_opengl3.cpp
#	examples/imgui_impl_sdl.cpp
#	examples/imgui_impl_vulkan.cpp
#	examples/imgui_impl_win32.cpp
#	imgui.h
#	imgui_demo.cpp