Add route_type/agency filtering to route viewer

[landonreed]

For feeds with large numbers of routes, especially when multiple feeds/agencies are present, we should provide controls to filter on route_type and agency.

After further team discussion on this:

• The "filters" will just be standard dropdown selectors allowing the selection of either All Modes/Agencies or a single mode/agency.
• For styling, we'll just use the dropdown selector from the otp-ui form (currently used for setting things like max walk distance)
  

Desktop view

Mobile view

[binh-dam-ibigroup]

Closing this issue, it was fixed by #435.