Merge pull request #15 from cs198/help-requests

Help requests
use travis postgres for testing rather than heroku
Merge pull request #16 from cs198/travis-postgres

use travis postgres for testing rather than heroku
add validation for nonduplicate user checkins
tests for uniqueness
Return helpercheckin objects instead of people. TODO: nest people
modify routes for helpers
implement helpercheckin create, destroy
implement show
add checkout time to schema for helper checkins
return 200 on deleting already deleted checkin for idempotency; set checked out time
add another active staff member fixture
add create controller unit tests
add test for delete
test show, checkins
add integration tests for helper checkins
Merge pull request #14 from cs198/helpers-routes

Helpers routes
add jbuilder dep
fix enrollments plurality in HelpRequests model
add position method