Eamena 108 al ula permissions updates

[mradamcox]

Description of Change

Implements all of the group-based permissions levels that are described in #108.

Additional notes:

• Group membership levels are read < edit < editplus. However, they should be treated cumulatively, so if a user is given editplus membership, they must also be added to read and edit groups.
• The anonymous user must be removed from the read group.

Issues Solved

#108

Types of changes

• Bugfix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)

Checklist

• Unit tests pass locally with my changes
• I have added tests that prove my fix is effective or that my feature works
• I have added necessary documentation (if appropriate)