Implemented the 'User' persistent object.

also, added the 'server_id' field to all synced tables in the database.
Implemented the 'Field' ORM object.

also added the field 'url_encoded_value' to the 'field' table.
Implemented 'UserLink' & 'UserSection' ORM objects.
Refactor the persistence layer.
Implemented the Domain Model infrastructure.

Implemented the database access infrastructure.
Implemented the 'User' domain model.
Implemented the 'findUser' method in the 'Repository'.