Added New Database Functionality

This adds the ability to add a new database when one doesn't already
exist.  The other DB opening/closing/deleting functions will come
next.  The database is just stored as an encrypted JSON string using
the user's password.  At some point I'll also potentially spread that
string out across multiple top-level storage keys (hence the use of
'0' as the storage key for now) to avoid hitting per-key storage
limits with synced storage.  I'm also using single-character object
keys in the database (with constants, of course, for sanity's sake) to
save space and avoid hitting the overall storage limit any faster than
necessary if a user has a lot of passwords.