Version transitionType as a new property

It is exposed in the QtQml.StateMachine import, but note that the metaobject
version is just incremented (no need to match QtQml.StateMachine, which
is in a different module).

Change-Id: I50773d9dec5252aa93846b7e5f743958ee838023
Reviewed-by: Simon Hausmann <simon.hausmann@theqtcompany.com>