Add dep MMPickerView
Add party filter to home view

New flow:
  - Blank on first launch
  - User selects address
  - If error:
    - Hide GO! button
    - Hide party picker
    - Show error view and set error text
  - If partisan contests:
    - Display party picker
    - Display GO! button after user selects a party
    - Display GO! button automatically if user has already
      selected a party
  - If no partisan contests:
    - Display GO! button
      - Shift GO! button up to the space the party picker normally
        occupies
Add party filter choice to ballot view
Localize string dates in election view headers

Fix tests
Merge branch 'feature/party-filter' into develop