Implement User Groups and Permissions management

[maltezacharias]

For future developments, access control needs to be more specific than just student hospital staff

Use Django authentication:
https://docs.djangoproject.com/en/3.0/topics/auth/default/#user-objects
https://docs.djangoproject.com/en/3.0/topics/auth/default/#topic-authorization

• Create groups: superuser, manage_hospitals, manage_newsletter, view_statistics, student, hospital
• Create suitable permissions or use default model permissions if applicable and assign to groups
• Check if django admin is sufficient for authorization management
• Customize django admin for user objects and add search by username and/or e-mail: according to https://docs.djangoproject.com/en/3.0/ref/contrib/admin/#django.contrib.admin.ModelAdmin.search_fields

[maltezacharias]

Also: Where applicable check for the new authorizations:

• Newsletter
• Staff page
• Hide/Show Menu items depending on authoriations
• Replace isStudent isHospital checks by auth checks
• Migrate isStudent isHospital fields to authorizations
• Both statistics pages

[Baschdl]

Added view_statistics

[Baschdl]

@maltezacharias This issue is a blocker for releasing the statistics pages to the rest of the m4h team. Maybe high-priority?

[feeds]

what do you mean by 'authorizations'?