Views Caching Change

[rich-hart]

The constants used to define caching in views.py use public and no-caching headers for any request method which is authenticated to keep user data private and to prevent issues such as #206 / openstax/webview#955 . Could we still keep user data private and take advantage of caching for authenticated views methods by changing NO_CACHE to NO_CACHE = (None, {'public': FALSE}) or TIMED_CACHE= (datetime.timedelta(...), {'public': False})?