ges-launch: Add support for transition types
Currently ges-launch-1.0 doesn't allow setting transition types, the idea in term of CLI is adding something like:
ges-launch-1.0 +test-clip blue d=10 name=first +test-clip red s=5 d=10 name=second set-transition-type foo [element-name=first+second]We should set transition names with a well defined format and document that.