Feature Flags

I've only implemented this for controllers so far but we can use this in future for things like new x.y releases and keep pushing to master (not a task/31x-website and task/31x-release branch) but simply disable it.

I also want to give it a small admin panel so we can easily enable and disable these features live and locally which will also mean we can do quick reverts when live and for non-db editing (creating new tables etc. is fine) stuff we can also enable these feature flags for team members but not for the community making it easier to test and deploy. It also opens up A/B testing with real users.

- [x] Feature Flags Interface
- [x] Static Feature Flags
- [x] Controllers
- [ ] Twig function
- [ ] Services
- [ ] Simple ACP using doctrine
- [ ] File for config for feature flags
- [ ] Allow for enabling for some requests but not others (after this PR)