In the main menu the ImGui/SDL/System cursor was only drawn when it was
over an ImGui window, so only the Doom3 cursor is shown when outside
of ImGui windows.
The only problem with this is that the Doom3 cursor is only shown in
the parst of the window actually covered by the main menu, not the black
bars that are drawn on the left/right for widescreen-resolutions when
scaling the menu to 4:3 is enabled (which it is by default).
So now the ImGui cursor is also drawn when the cursor is on those
black bars (if any).
Also tweaked the windowtitle background colors a bit.
* Binding menu makes sure that the AllBindingsMenu always gets focus
when opened
* Give binding-related popups slightly rounder edges
* Move Game Options tab behind Video and Audio Options
* Make warning overlays a bit less translucent
Pause the game (with g_stopTime) when the settings menu is opened
while ingame, unpause it when it's closed.
If the menu is open while ingame and an ImGui window has focus,
the mouse cursor is shown. If the player clicks outside an ImGui window,
it gets unfocused and the cursor is hidden and the player can look
around. Pressing F10 (or whatever key is bound to "dhewm3Settings")
will give focus back to an open ImGui window, pressing it again then
will close the settings window, pressing it once again afterwards will
open the settings window again.
handleMouseGrab() (in sys/events.cpp) now checks if sys_imgui thinks
that a cursor should be shown (via D3::ImGuiHooks::ShouldShowCursor())
and if so, shows it and ungrabs the mouse. This, together with
D3::ImGuiHooks::NewFrame() checking ShouldShowCursor() to (unset)
ImGuiConfigFlags_NoMouseCursorChange, should prevent flickering cursor
problems that sometimes occurred when ImGui's SDL2 backend and dhewm3
disagreed on whether the cursor should be visible.
Also fix MSVC build: For some reason Microsoft's sad excuse of a compiler
only sets __cplusplus to a value from this millenium if the
/Zc:__cplusplus compiler option is set, but that's only supported from
VS2017 15.7 on. The alternative is to use _MSVC_LANG, which always holds
the version that __cplusplus *should* have...
