feat: add in-app settings for the individual hacklab to configure

[braaar]

I propose that we implement a settings panel designed to allow individual hacklabs who are using mulysa to adjust some global settings for their instance of mulysa. In my mind this should remove the need for forking the repository.

Things that would belong in these settings:

• Basic information about the hacklab
  • Name
  • Email
  • Other contact information
• Toggling on and off various features (such as feat: introduce a balance model #425 if that is implemented)
• Configuring various features
• Email templates?
• etc.

Implementation
We could use django-constance for this, or just store the data in a Singleton model. I think django-constance seems like a good choice. It integrates with django admin and does a lot of the basic stuff for us.