Implement EfServices loading cache from common

I noticed an odd pattern in the InterestGroupResource where it is injecting the default IG service directly. The mock IGService then extends this default and adds mock data to it on startup.

There was an InterestGroup-related test failure while trying to build membership with Jenkins. I think this may be related.

We should move away from this pattern and mock the IGAPI directly. This is a good time to leverage the new LoadingCacheService in commons for IG data, as well as for any other services that pre-load data on startup.