Make exit via 'q' key work again in Blinkenlights UI

With the new abort signal handler, we can send a signal that lets us
exit cleanly. Make use of this, rather than crashing out in ugly ways.

This affects only the Blinkenlights UI when pressing 'q'.

Signed-off-by: Sebastian Spaeth <Sebastian@SSpaeth.de>

offlineimap/ui/Curses.py

@@ -487,11 +487,9 @@ class Blinkenlights(UIBase, CursesUtil):
         if key < 1 or key > 255:
             return
         if chr(key) == 'q':
-            # Request to quit.
-            #TODO: this causes us to bail out in main loop when the thread exits
-            #TODO: review and rework this mechanism.
-            currentThread().set_exit_exception(SystemExit("User requested shutdown"))
-            self.terminate()
+            # Request to quit completely.
+            self.warn("Requested shutdown via 'q'")
+            offlineimap.accounts.Account.set_abort_event(self.config, 3)
         try:
             index = int(chr(key))
         except ValueError: