Improve transition between plugin and WPS

Eliminate flashing when plugins are launched
from WPS, by not enabling the SBS, and by
deferring other lcd updates.

Also prevents flashing root menu activity when
returning from plugins.

Change-Id: I7d761867027f2275c4ab8e16ada3107c7ba0be6e

apps/misc.c

@@ -1579,6 +1579,13 @@ void push_current_activity(enum current_activity screen)
     }
 }
 
+void push_activity_without_refresh(enum current_activity screen)
+{
+    current_activity[current_activity_top++] = screen;
+    FOR_NB_SCREENS(i)
+        skinlist_set_cfg(i, NULL);
+}
+
 void pop_current_activity(enum activity_refresh refresh)
 {
     current_activity_top--;