Refactor: Added empty imgui_widgets.cpp + updated project files / makefiles etc. accordingly (#2036)

Merge branch 'master' into viewport ...

# Conflicts:
#	examples/example_glfw_opengl3/main.cpp
#	examples/imgui_impl_opengl3.cpp
#	imgui.cpp
#	imgui_internal.h

Examples: Vulkan: Minor tweaks.

Examples: OpenGL: Added support for glew and glad OpenGL loaders out of the box. (#2001, #2002). Changelog, tweaks, applied changes to SDL+OpenGL3 example.

WIP on configurable OpenGL loader. (#2001, #2002)

Examples: Vulkan: Viewport: Tweak to improve framerate on multiple-viewport situations, tho it is still halving the unthrottled framerate on nvidia for some reason.. Followup to 4dea032 (#1542)

Merge branch 'master' into viewport ...

# Conflicts:
#	imgui.cpp
#	imgui.h

Examples: Vulkan: Fixed handling of VkSurfaceCapabilitiesKHR::maxImageCount = 0 case. Tweaked present mode selections.

Examples: Viewport: Disabling swap intervals / vsync on secondary context to match what the DX11 bindings is doing. (#1542)

Merge branch 'master' into viewport ...

# Conflicts:
#	examples/imgui_impl_vulkan.h
#	imgui.cpp

Examples: imgui_impl_vulkan: Comments (re)

Examples: imgui_impl_vulkan: Comments

Viewport: DestroyPlatformWindows() checks for the bool CreatedPlatformWindow flag correctly. Note that we set CreatedPlatformWindow=true for the main viewport to allow the back-end to store data in the public Viewport structure (for consistency). (#1542)

Merge branch 'master' into viewport ...

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

Examples: Cast to ImTextureID instead of void* when assigning to TexId. Applied to all examples. (#2015)

imgui_impl_dx12: Cast to ImTextureID instead of void* to enable redefinition of ImTextureID (#2015, #301)

imgui_impl_opengl3: Advertised as a ES2/ES3 renderer. Defaults to ES3 on Android. Default on "#version 300 es" on ES 3. (#2002, #1873)

imgui_impl_win32: Don't redefine WIN32_LEAN_AND_MEAN if already defined (#2014)

Examples: Fix 'How to build' instructions for SDL2 examples (#2012)

imgui_impl_opengl3.cpp Using GLES3 on IOS instead of gl3w. (#2002, #1873) ...

Not modifying the main.cpp yet because we need to test GL ES 3 context creation on iOS (only imgui_impl_opengl3.cpp was tested).

Examples: OpenGL2: Disabling/restoring GL_LIGHTING and GL_COLOR_MATERIAL to increase compatibility with legacy OpenGL applications. (#1996)

Merge branch 'master' into viewport ...

# Conflicts:
#	examples/imgui_impl_dx11.cpp
#	examples/imgui_impl_glfw.cpp
#	examples/imgui_impl_sdl.cpp
#	imgui.cpp

Changelog for #1989

imgui_impl_dx11: Using ID3D11Factory instead of ID3D11Factory1 (#1989)

imgui_impl_glfw, imgui_impl_sdl: Workaround for Emscripten which doesn't seem to handle focus related calls. (#1941)

Added Visual Studio 2017+ build cruft to Ignore List (.vs/ folder)

Merge branch 'master' into viewport ...

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

imgui_impl_opengl3: Comments. (#1987)

Examples: imgui_impl_opengl3.cpp Using #ifdef GL_SAMPLER_BINDING instead of if (glBindSampler) (#1985)

Examples: imgui_impl_osx: Fix for incorrect DeltaTime calculation on mac OS. (#1978)