Merge branch 'master' into docking

# Conflicts:
#	backends/imgui_impl_dx10.cpp
#	backends/imgui_impl_dx9.cpp
#	backends/imgui_impl_glfw.cpp
#	backends/imgui_impl_metal.mm
#	backends/imgui_impl_opengl2.cpp
#	backends/imgui_impl_opengl3.cpp
#	backends/imgui_impl_vulkan.cpp
#	imgui.cpp