Remove prefix completely

[drozzy]

I got rid of the prefix, replacing it with the $streams stream. This works for loading aggregates pretty well, which is all I really need. Allows me to do projections in Greg's EventStore correctly (e.g. by using $ce-aggregatename):

Did not test:

• event handlers
• process managers

[drozzy]

This certainly breaks tests.. not sure how to fix them. E.g.:

5) test subscribe to all streams should receive events appended to any stream (Commanded.EventStore.Adapter.SubscriptionTest)
     deps/commanded/test/event_store_adapter/subscription_test.exs:105
     No message matching {:events, received_events} after 5000ms.
     The process mailbox is empty.

[drozzy]

I also added a fix that set the extreme dep to ~> 0.11.0