OR-869 Remove userIsCommunityMember() in favor of isMember()

Those ware duplicate methods with the same intent.
Notre that the member lookup is done against the passed community object, so:
- it doesn't issue a datastore request
- but the community object have to be up to date for the result to be accurate
OR-869 Remove authorization middleware requiresCommunityMember method

and change the community middleware isMember name to requiresCommunityMember
Merge pull request #593 in OR/rse from ~MBAILLY/rse:OR-869-remove-community-isMember-dups to master

* commit 'a047d9fd84edaacaf37566db4b306afaf0f3e6a4':
  OR-869 Remove authorization middleware requiresCommunityMember method
  OR-869 Remove userIsCommunityMember() in favor of isMember()