Decouple codidact from code

[Taeir]

This pull request decouples the codidact network from a lot of the pages. It does so by defining a helper function which checks the domain of the community for .codidact.[com|org]. It then disables or changes components on pages based on this setting.

TODO

• [ ] Special config file for these settings that do not change often or at all?
• [ ] Email addresses as settings
• [ ] Figure out something for the copyright in the mailer and devise mailer (layout)
• [ ] Network name setting?

Fixes #826

[cellio]

Thanks for working on this! I knew we only got some of them (the easiest ones, naturally) in the previous sweep, and then I lost track of it.