Introduce new User permission: Super User Access

[mattab]

The feature to be able to have several Super Users is becoming more important, and many users have requested it in the forums and in #2589

Tasks:

• Create superAdmin permission. The superAdmin permission is equivalent to the currently "superUser" in terms of power.
• The user stored in the config file has always superAdmin permission.
• Code: change all calls to checkUserIsSuperUser to: checkUserHasSuperAdmin permissions, setUserIsSuperUser becomes setUserHasSuperAdmin, checkUserIsSuperUserOrTheUser -> checkUserIsTheUserOrHasSuperAdmin
• Add / update unit tests

Note:

• the Super User stored in the config file will never lose its super admin capability. But other users with SuperAdmin permission can lose it
• The UI for setting Super Admin permission is out of scope, it is covered in Add Support for Multiple Superusers #2589

[tsteur]

In e4b425b: refs #4564 #2589 added possibility to define multiple superusers

[tsteur]

In 743d7b8: refs #4564 #2589 do not allow to edit a users websites permissions if user is superuser. Reload page after successfully changing superuser permission to make sure it is afterwards possible to (edit / not edit) websites permissions

[tsteur]

In 265f4b9: refs #4564 #2589 we need a small difference between superUser and configSuperUser

[tsteur]

In 743b92d: refs #4564 some more fixes for config super user

[tsteur]

In bdb6967: refs #4564 restrict sites to login for all non super users

[tsteur]

In bda7796: refs #4564 also check for the config user

[tsteur]

In 81e7f87: refs #4564 introducing new methods to make user a user has superuser access. Old methods will still work but are marked as deprecated and they will be removed in a future release

[tsteur]

In df54712: refs #4564 introducing some more new methods for has superuser access. Old methods will still work but are marked as deprecated and they will be removed in a future release

[tsteur]

In cae8ff4: refs #4564 added test to make sure the deprecated methods will be there as promised and removed afterwards

[tsteur]

In d8a69b1: refs #4564 fixed some permission issues and removed the todo tags

[tsteur]

In ff36d5e: refs #4564 added missing method again to not break API and fix tests

[tsteur]

In ea48bba: refs #4564 added db update (version number needs to be changed later probably) and renamed more methods

[tsteur]

In 71bf5fe: refs #4564 added column superuser access

[tsteur]

In 0ffbe10: refs #4564 fix sql

[tsteur]

In 57a1824: refs #4564 fix adding anonymous user is not possible