Creator dashboard service calendar CRUD

[rconjoe]

Carefully keep track of the create/read/update/delete flow for sessions from potential through publish: the database operations for this are split across the API (node admin SDK) and the frontend firebase JS sdk. i.e. potential sessions are written from the frontend app directly to the database. This flow should be robust, making sure that no edge cases "confuse" the API or mess up data structures even in weird user input scenarios.