Add background-image to highlighted cards

Also fix background-image for Chrome
Add EventType
Add EventType migrations
Refactor events and notes hierarchy
Reuse slug code
Start code migration from NoteType to ApplicantEventType
Refactor ApplicantEventType
Change ApplicantNoteType by ApplicantEventType in UI
Remove ApplicantNoteType and dependents
Fix ApplicantEventType migration
Working on show applicants flow in cards
Allow to search applicants by event type slugs

TODO: related UI and remove obsolete fields
Allow to filter by eventTypes
Merge pull request #259 from andresmoschini/highlighted-applicants

Add background-image to highlighted cards
Show event-types checkboxes as buttons
Apply responsive layout without filter by bootstrap-scope
Just in case of we decide to usea a vertical button group
Remove obsolete HaveInterview and HaveTechnicalInterview fields
Merge pull request #261 from andresmoschini/applicants-search-flow-state

Applicants search flow state
Showing flow events on applicant cards