Set cache-control headers using flask-cache.

Add constant times in cache_time.
API: Remove instance of hardcoded emails.

We have the roles framework now; no need to
hardcode an e-mail check.
PEP8 fixes.
Travis: Add cache_type.
Requirements: Add flask-cache.
Users views: Remove unneeded imports.
Merge pull request #191 from CalPolyIEEE/set-expires-headers

Set expires headers on view responses.