MWEB-667

**DO NOT MERGE -- MOBILE WEB TEAM WILL CR AND QA IT FIRST**

* bunch of unit tests for existing PHP entry points,
* moved some existing logic from one place to another,
* added new `WikiaInteractiveMapsPermissionException`,
* implemented logic which disallows blocked user to create/delete/change maps.
Yep, good catch! Thanks :+1: