Implement _NET_WM_STATE_STICKY, bound to CM-s by default; allows any

client to 'stick' to all desktops (ewmh speak) or groups - this
currently has the same affect as setting a client's group to 'nogroup',
with the exception that the client can also be in a group, so when
un-sticking, the client will go back to its original group/desktop.

kbfunc.c

@@ -432,6 +432,12 @@ kbfunc_client_movetogroup(struct client_ctx *cc, union arg *arg)
 	group_movetogroup(cc, arg->i);
 }
 
+void
+kbfunc_client_sticky(struct client_ctx *cc, union arg *arg)
+{
+	client_sticky(cc);
+}
+
 void
 kbfunc_client_fullscreen(struct client_ctx *cc, union arg *arg)
 {