Refactor recording api methods and fix logic

Refactored code of recording api setup, teardown, and
endpoint functions.

Added a get_current_state_str() method to Multimedia to make some code
in recording api cleaner.

Fix to recording api logic determining next_id.
Fix to test_server.py teardown to undo patching to media_dict

closes #629
Scratch that, I just remembered that `media_info` is a shelve object. But you can still condense the second pair of assignments.