Move the installed includes to a subdir

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

src/core/display.c

@@ -34,21 +34,21 @@
 
 #include <config.h>
 #include "display-private.h"
-#include "util.h"
-#include "main.h"
+#include <meta/util.h>
+#include <meta/main.h>
 #include "screen-private.h"
 #include "window-private.h"
 #include "window-props.h"
 #include "group-props.h"
-#include "frame-private.h"
-#include "errors.h"
+#include "frame.h"
+#include <meta/errors.h>
 #include "keybindings-private.h"
-#include "prefs.h"
+#include <meta/prefs.h>
 #include "resizepopup.h"
 #include "xprops.h"
 #include "workspace-private.h"
 #include "bell.h"
-#include "compositor.h"
+#include <meta/compositor.h>
 #include <X11/Xatom.h>
 #include <X11/cursorfont.h>
 #ifdef HAVE_SOLARIS_XINERAMA
@@ -417,7 +417,7 @@ meta_display_open (void)
   /* A list of all atom names, so that we can intern them in one go. */
   char *atom_names[] = {
 #define item(x) #x,
-#include "atomnames.h"
+#include <meta/atomnames.h>
 #undef item
   };
   Atom atoms[G_N_ELEMENTS(atom_names)];
@@ -490,7 +490,7 @@ meta_display_open (void)
   {
     int i = 0;    
 #define item(x) the_display->atom_##x = atoms[i++];
-#include "atomnames.h"
+#include <meta/atomnames.h>
 #undef item
   }