Goodbye spammer integration #775

I've started with intergrating Goodbye Spammer into the core. Please don't merge this!

It's working but there are still a few things I want to optimise.

Todo:
- [x] use the new get_input method
- [x] New Button at the top of the table (https://github.com/MattRogowski/Goodbye-Spammer/pull/1)
- [x] Modify the overview (remove the checkboxes, only show what will be removed)
- [x] Find a solution for upgrading MyBB (rename everything or uninstall Goodbye Spammer)
- [x] add new things for 1.8 (eg I'll need to look at the new report center)
- [ ] test everything carefully
- [x] add plugin hooks

Feel free to test this PR and to give feedback

Issue: #775