Issues/135/remove duplicate db keys

[prphntm63]

Ok boiz, buckle up - this one's a doozy

• Fixes 135 (for real this time)
• Fixes #64
• Fixes #85
• Fixes #92

Changes:

• Refactored Sequelize models to use associations properly
• Added migration to remove redundant keys and implement Sequelize association keys
  • From Scoresheet: All user info (including UserId), all flight info. Changed flight_key to FlightID, flight_total removed (dynamically calculated from Flight)
  • From Flight: Changed created_by to UserId
• Refactored a TON of things to use UserId in Flight instead of scoresheet to avoid having a duplicate UserId

Tests:

• Migrations and new schema tested with sqlite3 and Postgres locally

[prphntm63]

• Added a sanitize() instance method on the User model
• Removed console.log()