Create postgres array field for Customer mobility impairments on trip tickets; drop trip_tickets.mobility_type_id field

* Move ethnicity to a free text field on trip tickets. WIP #1201.
* adding ar_pg_array gem to enable support for postgres array data type
* Swapping out ar_pg_array gem for activerecord-postgres-array
* Adding customer_mobility_impairments field to TripTicket, along with associated unit test
* Refactoring some of the customer_identifiers attribute code and adidng a missing test
* Adding fields for customer_mobility_impairments to trip ticket form
* Adding javascript enhancements to customer_mobility_impairments fields
* Removing mobility_type_id field from trip_tickets
Merge branch '1202-customer-mobility-impairments'

Conflicts:
	db/schema.rb