CppEditor: Add quickfix to convert to new style connect()

Limitations:
 * Overloads are not yet handled
 * Action is not offered if the slot can't be looked up in the
   receiver expression (e.g. when it's a base class pointer).

Change-Id: I5779ff1b74657025d058d4f3690f6723b4784497
Reviewed-by: Nikolai Kosjar <nikolai.kosjar@digia.com>