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>

libdivecomputer.h

@@ -17,10 +17,12 @@ typedef struct device_data_t {
 	unsigned int deviceid, diveid;
 	dc_device_t *device;
 	dc_context_t *context;
-	progressbar_t progress;
 	int preexisting;
 	gboolean force_download;
+#if USE_GTK_UI
+	progressbar_t progress;
 	GtkDialog *dialog;
+#endif
 } device_data_t;
 
 extern GError *do_import(device_data_t *data);