Update cache usage to reduce cache entry volume

As discussed in a call with Martin earlier, caching each individual result from fdndb-api, ldap, and accounts-api for every profile request will create too many cache entries once the service is live, chewing through our resources. To eliminate this problem, we should cache the final EfUser object built from all the appropriate data.

This work will need the use of the new caching implementation mentioned here: eclipsefdn-api-common#91 (closed) This work will be done in parallel.