Improve Persistence

[Bibo-Joshi]

Originally intended to close #1671 , this now does 3 things:

1. Unify the two methods of dispatcher used to update the persistence. This makes sure that
   1. If persistence is updated after handling an update, only the corresponding user/chat_data is updated
   2. Errors that appear when updating persistence on shutting down the bot will be handled correctly
2. Fixing a minor bug in Pickle/DictPersistence: When calling update_*_data before calling get_*_data, we need to check that the internal attributes are not None
3. Actually close [FEATURE] Persistence inside of Jobs #1671 by updating the persistence after running a job

[Bibo-Joshi]

CI:

• Py3.7 fails on test_game_score. Unrelated
• Codecov mainly complains that the parts

'Saving user data raised an error and an ' \
'uncaught error was raised while handling ' \
'the error with an error_handler'

are not tested. But as far as I can see, they weren't tested before …
Added corresponding tests b/c more coverage = more better 🤸‍♂

[Poolitzer]

LGTM