Rework venue address storage

[rlmead]

Database

• ✅ Split address column into street, city, state, zip, neighborhood
  • Look into standard ways of handling addresses in Postgres (some ideas here)
• ~Figure out how to reliably wrangle the existing data into the new format~
  • See #350

Back end

• :white_check_mark: Handle new address format

Front end

• :white_check_mark: Handle new address format on venue submission
• :white_check_mark: Handle new address format on admin venue interface
• :white_check_mark: Add new combobox input field: State
  • Suggest Kentucky and the bordering states
• :white_check_mark: Make City input into a combobox, too
  • Suggest the cities that are most common in our existing data