WIP: lib & db restructure

[nhamilakis]

Major restructuring to correspond better to the zerospeech v2 structure

• rename root modules for clarity (lib => core, db => data)
• refactor db.q => model_queries as to unify models & queries
• remove _fs module (it was confusing) and move items directly into lib & model_queries as to have a more object oriented approach.
• move sql table definitions into a table.py into the vocolab.data module (it was confusing being with the model classes)
• create a new model table to allow handling of model id's
• check how refactoring altered user interactions (user_lib)
• check how refactoring altered challenge management (challenge_lib)
• cleanup vocolab.core.leaderboard_lib to be independent than submissions
• create a method that allows importing leaderboard entries directly (mark them as archived if submission is not present)
• rework submission as to allow archival & importing
• create model management admin commands
• test new upload system
• deactivate auto-eval (temporarily)
• Refactor submission_lib
• Get API ready for deployment
• READ-ONLY mode

This pull request will resolve #27 #19 #11