Drop down for user to select water agency (in addition to address)

[patwater]

Would be useful to have a simple dropdown for users to select their water district in the bill calculator tool in addition to the address box. Not mission critical though makes the bill calculator tool more useful for water managers looking to see a given districts rates and makes the bill calculator a more interactive replacement for the appendix listing water rates from the 2015 survey. CC @christophertull

https://demo.californiadatacollaborative.com/BillCalculator/BillCalculator_RateParser_AddressInput/