This will be used to replace some of the hooks that are used to call
into window.c, so that the workspace index property is properly kept up
to date.
We can't name the property "index" since it causes conflicts with the
meta_workspace_index method. This should really be called
meta_workspace_get_index, but oh well.
If mutter is going to be a "real" library, then it should install its
includes so that users can do
#include <meta/display.h>
rather than
#include <display.h>
So rename the includedir accordingly, move src/include to src/meta,
and fix up all internal references.
There were a handful of header files in src/include that were not
installed; this appears to have been part of a plan to keep core/,
ui/, and compositor/ from looking at each others' private includes,
but that wasn't really working anyway. So move all non-installed
headers back into core/ or ui/.
https://bugzilla.gnome.org/show_bug.cgi?id=643959
