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/api.c

@@ -54,6 +54,7 @@
 #include "plugins/settings.h"
 #include "plugins/disco.h"
 #include "ui/ui.h"
+#include "ui/win_types.h"
 #include "ui/window_list.h"
 #include "xmpp/roster_list.h"
 
@@ -205,6 +206,13 @@ api_get_current_recipient(void)
     }
 }
 
+gchar*
+api_get_current_window(void)
+{
+    ProfWin* current = wins_get_current();
+    return win_get_title(current);
+}
+
 char*
 api_get_current_muc(void)
 {