Improve search edge cases

Handle an edge case where the user may search "Full Time" jobs then changes the type to "All Jobs." Previously, the filter would just go away when switching to "All Jobs."

Also return a promise from `find` for companies in the afterModel hook. Previously, visiting the page with a query param matching a company name failed because companies were not yet resolved by the time _filter is initially called.

There's one caveat with the test though that I can't seem to figure out. The test will fail the first time, but if you refresh the qunit page it will pass every other time. I know the feature actually works though because it works every time when I try it out manually in the app. I think I may be overlooking some setting in ember-testing.