This improves our completion support for documentation
comments. It's now possible to have a Doxygen block
generated when hitting enter after a /** or /*! comment
start. A couple other related options are also available.

Task-number: QTCREATORBUG-2752
Task-number: QTCREATORBUG-3165

Change-Id: I1c81c0b4b370eb1d409ef72a9c7f22c357f202f4
Reviewed-by: Leena Miettinen <riitta-leena.miettinen@nokia.com>
Reviewed-by: Christian Kamm <christian.d.kamm@nokia.com>