Refactoring of permission code

If you look at the CRM_Contact_BAO_Contact_Permission you'll see that if we want to check individual permissions we only have the ::allow() method which we would have to call for each contact individually - and this call is actually quite expensive.

In a context like PR-9193 this would mean 50+ calls and a serious performance problem.

Therefore I did the following (after talking to Eileen McNaughton in the Edale sprint):

1. I created a method ::allowList() that can batch process contact_ids for permissions
2. I added the respective unit tests
3. By doing that I found and fixed two bugs in the original code