Modify LocalSettings.php for new groups management

* Clean code
* Add new mapping
* Remove all rights granted directly

Change-Id: I9a8ab84bef3701e909d57b5e4005e04d7a411437
Create a dedicated groups mapper

Change-Id: Ia5141580342cc961d616f48dab0df30a458e5573
Add system event actions for Mediawiki groups

Change-Id: Iea1792d66c660767dffbf7a37888dabb0cecf4b9
User is renamed in Mediawiki during SYSTEM_EVENT

Change-Id: I96627ee39b3f53ccda19046180e20ae07e2e3339
Remove "create an account" link for anonymous users

Change-Id: Idb2eb50f22cd1b5bd3356713f20d7bd55ca00d08
Merge remote-tracking branch 'gerrit/5916_mapping_between_mediawiki_and_tuleap_groups' into HEAD

* gerrit/5916_mapping_between_mediawiki_and_tuleap_groups:
  Remove "create an account" link for anonymous users
  User is renamed in Mediawiki during SYSTEM_EVENT
  Add system event actions for Mediawiki groups
  Create a dedicated groups mapper
  Modify LocalSettings.php for new groups management

Change-Id: If8072c19e17a3c8ee375856b2b36f668bd88c0dd
This is Tuleap 6.9.99.31

Change-Id: Ia113770e8ae7c31c36440e671f179370f39f98c5