Remove unneeded events / states from BloCs

[Boehrsi]

Is your feature request related to a problem? Please describe.

In the beginning we weren't aware of yield* and created a lot of useless event / state transitions (as seen here https://github.com/open-xchange/ox-coi/blob/develop/lib/src/contact/contact_change_bloc.dart).

Describe the solution you'd like

Instead of adding events, which directly map to new state, e.g. if a method in a BloC is finished, we should just directly return the new state and use it via yield*. Compare https://github.com/open-xchange/ox-coi/blob/develop/lib/src/contact/contact_list_bloc.dart

Internal Bug Tracker.

[Boehrsi]

Will be merged after the final beta-7 release. As this could introduce side effects.