Add flat file datastore

[Jearil]

Sqlite3 has threading issues which prevents us from reading/writing to the database using multiple threads even if we do our own locking. This is to try making an alternative data store based on the filesystem. Data will be stored in a simplenosql/ directory in the data directory of the app. Buckets will be subdirectories of that, and each entity will be a file with the entityId equaling the filename (or a sha1 hash thereof).

The directory structure should look like:

simplenosql/
  bucket1/
    <SOME40CHARACTERHASH>
    <SOME40OTHERCHARACTERHASH>
  bucket2/
    <SOME40CHARACTERHASH>