feat(api): add get_current_window call

Add prof_get_current_window API to retrieve the title of the currently active window, matching the titlebar display.

The feature is especially useful to track currently used plugin window.

src/plugins/profapi.h

@@ -71,6 +71,7 @@ void (*prof_notify)(const char* message, int timeout_ms, const char* category);
 void (*prof_send_line)(char* line);
 
 char* (*prof_get_current_recipient)(void);
+char* (*prof_get_current_window)(void);
 char* (*prof_get_current_muc)(void);
 int (*prof_current_win_is_console)(void);
 char* (*prof_get_current_nick)(void);