FEATURE Add nextReviewDate on card for better review process

[mfaust35]

• Update room_version to 2.2.2
• Update card model: remove attribute last_seen, add attribute next_review, add attribute updated_at and keep created_at
• Card model can delegate automatically method on roster: instead of card.roster.find { ... } you can call card.find { ... }. It does not always makes code clearer, so I kept calling card.roster.something() when needed
• Card model now expose method to change CardContent and update rating which return a copy. Previously anyone outside Card was messing up with cards attributes. It is now more controlled
• Add databaseVersion4 schema, migration, and tests
• Remove method updateCreatedAt from cardDao (update now pass through regular update method)
• Refactor file CardRoomDataSourceTest into unitTest

Fixes #18