Remove the majority of the Gtk related code

- rip all Gtk code from qt-gui.cpp
- don't compile Gtk specific files
- don't link against Gtk libraries
- don't compile modules we don't use at all (yet)
- use #if USE_GTK_UI on the remaining files to disable Gtk related parts
- disable the non-functional Cochran support while I'm at it

Signed-off-by: Dirk Hohndel <dirk@hohndel.org>

linux.c

@@ -1,6 +1,7 @@
 /* linux.c */
 /* implements Linux specific functions */
 #include "dive.h"
+#include "display.h"
 #include "display-gtk.h"
 #include <gconf/gconf-client.h>
 #include <string.h>