Add method to check if a user is in a certain group
Add method to check if a user is in a certain group

This is an extension to the api that the groups module provides to other
modules. In some modules it can be convenient to check if a user is in a
certain group.

I already submitted this once, but was asked to resubmit for 3.7, see
https://github.com/forkcms/forkcms/pull/698

jeroendesloovere/forkcms,Thijzer/forkcms,wengyulin/forkcms,Saxithon/gh-pages,sumocoders/forkcms,dmoerman/forkcms,Saxithon/gh-pages,matthiasmullie/forkcms,mathiashelin/forkcms,justcarakas/forkcms,Katrienvh/forkcms,vytenizs/forkcms,bartdc/forkcms,sumocoders/forkcms,vytsci/forkcms,Katrienvh/forkcms,Thijzer/forkcms,forkcms/forkcms,riadvice/forkcms,riadvice/forkcms,matthiasmullie/forkcms,jonasdekeukelaere/forkcms,vytenizs/forkcms,Katrienvh/forkcms,vytenizs/forkcms,carakas/forkcms,WouterSioen/forkcms,vytsci/forkcms,jeroendesloovere/forkcms,carakas/forkcms,jessedobbelaere/forkcms,ikoene/forkcms,jacob-v-dam/forkcms,DegradationOfMankind/forkcms,wengyulin/forkcms,forkcms/forkcms,jacob-v-dam/forkcms,carakas/forkcms,DegradationOfMankind/forkcms,jonasdekeukelaere/forkcms,vytsci/forkcms,dmoerman/forkcms,jeroendesloovere/forkcms,Katrienvh/forkcms,nosnickid/forkcms,sumocoders/forkcms,tommyvdv/forkcms,mathiashelin/forkcms,jeroendesloovere/forkcms,dmoerman/forkcms,jonasdekeukelaere/forkcms,jessedobbelaere/forkcms,bartdc/forkcms,riadvice/forkcms,wengyulin/forkcms,nosnickid/forkcms,riadvice/forkcms,jacob-v-dam/forkcms,sumocoders/forkcms,tommyvdv/forkcms,jonasdekeukelaere/forkcms,carakas/forkcms,jessedobbelaere/forkcms,nosnickid/forkcms,forkcms/forkcms,tommyvdv/forkcms,matthiasmullie/forkcms,bartdc/forkcms,forkcms/forkcms,Thijzer/forkcms,DegradationOfMankind/forkcms,mathiashelin/forkcms,ikoene/forkcms,DegradationOfMankind/forkcms,justcarakas/forkcms,sumocoders/forkcms,ikoene/forkcms,WouterSioen/forkcms,carakas/forkcms,mathiashelin/forkcms,jessedobbelaere/forkcms,justcarakas/forkcms,jacob-v-dam/forkcms,jonasdekeukelaere/forkcms,tommyvdv/forkcms