There were lots of places in the code that called Sys_GrabInput(),
some of them each frame.
Most of this is unified in events.cpp now, in handleMouseGrab() which
is called once per frame by Sys_GenerateEvents() - this makes reasoning
about when the mouse is grabbed and when not a lot easier.
Sys_GrabInput(false) still is called in a few places, before operations
that tend to take long (like loading a map or vid_restart), but
(hopefully) not regularly anymore.
The other big change is that the game now uses SDLs absolute mouse mode
for fullscreen menus (except the PDA which is an ugly hack), so the
ingame cursor is at the same position as the system cursor, which
especially helps when debugging with `in_nograb 1` and should also help
if someone wants to integrate an additional GUI toolkit like Dear ImGui.
Don't include the lazy precompiled.h everywhere, only what's
required for the compilation unit.
platform.h needs to be included instead to provide all essential
defines and types.
All includes use the relative path to the neo or the game
specific root.
Move all idlib related includes from idlib/Lib.h to precompiled.h.
precompiled.h still exists for the MFC stuff in tools/.
Add some missing header guards.
