Refactor Firebase calls into shared services

[bjsawyer]

There are lots of GET/PUT/POST calls to Firebase within our components that should really be pulled into services instead. We should be able to parameterize these functions to reduce all the duplicated logic and make things cleaner.

• Create service for each db table
• Inject AngularFire2 into services via constructor and remove from components
• Inject new services into components instead
• Create functions that call Firebase
  • GET
  • PUT
  • POST
  • DELETE
  • Object vs. List versions of each (?)
• TODO: Create issues to unit test these services

Question: Stick to subscriptions, or use async/await?