OR-578 Add a opts arguments to createCommunity helper

This opts object is merged into the community object before being injected
into mongoose Community constructor
OR-578 adds a membershipRequest property in community JSON on REST endpoints
Merge pull request #450 in OR/rse from ~MBAILLY/rse:OR-578-indicate-membership-requests-in-communities-JSON to master

* commit '4ee73f84a52ee467cc2492af78cac054e3ba5599':
  OR-578 adds a membershipRequest property in community JSON on REST endpoints
  OR-578 Add a opts arguments to createCommunity helper