Remove Broker code in V3

[jchate6]

• remove tom_alerts as an installed app
• Remove alerts from Nav Bar
• Management command needed to facilitate Dataservice queries. #1421
• disconnect buttons on the Target List Page and Target Detail Page
  • move functionality to Dataservices
• update settings.py template
• Update docs

Bonus:

• add method to customize what dataservices show up in the nav bar dropdown
• update apps

[jchate6]

• walk through and document migrations
  • need two releases
    • One release with tom_alerts in installed apps --> Migrate
    • 2nd release with squashed migrations and removed from installed apps
• Do we need a data migration (management command?) for ReducedDatum.Message -> ReducedDatum.source_name?
• Need to squash DataProduct migrations to remove reference to tom_alerts (tom_dataproducts.0011_reduceddatum_message)