Rename UserAccess to StoredUser
Add JSONStorer and tests for it.
Add StoredChannel and tests.

* Added JSONStorer to StoredUser struct.
Rename AddUser to SaveUser
Added StoredChannel to store.

* Added serialization to StoredChannel.
Add a NetworkID to StoredChannel.

- Users were stored with no networkID because they are meant to be
  cross-server. Channels however only exist on one server at a time and
  should not share storage data.