Display list of students on buses page
Fix session specs
Use Backbone.Collection.find over _.find
Render map on the buses page
Properly stub zonar API response

Use ERB template to paramterize response. Add BusLocation class for
wrapping Zonar response.
Create a BusLocation for every BusAssignment
Refactor api stubbing

Change the `connection` interface on the Zonar module so it can be
stubbed the same way as AssignmentSearch and ContactId. Refactor
stubbing methods to take a rack response_body.

Re-stub all connections on each spec run to ensure stubs are not used
across specs.