Add new command /changes

With that command one can see the modifications of the runtime
configuration vs. the saved configuration.

Signed-off-by: Steffen Jaeckel <s@jaeckel.eu>

src/config/preferences.h

@@ -204,6 +204,7 @@ typedef struct prof_winplacement_t
 } ProfWinPlacement;
 
 void prefs_load(const char* config_file);
+void prefs_changes(void);
 void prefs_save(void);
 void prefs_close(void);
 void prefs_reload(void);