Consistently use string indexing for registry prop

This makes the use of the registry as a dictionary more clear. It could
also prove important for certain code eliminations paths if someone ever
tries to use the Closure Compiler on Annotator.
Improve consistency of event timing

The 1.2.x series fired `beforeAnnotationCreated` before setting up the
annotation. We should do the same here, and be consistent in where in
the action lifecycle we fire the events for all of them.