Write a bot which changes current revisions

[kulla]

We should write a bot which we can run regularly (maybe once a year) which does certain jobs in formatting Serlo articles like:

• Canonicalize links api.serlo.org#1681
• Delete all equations plugins without any equations api.serlo.org#1680
• Remove all boxes without content api.serlo.org#1679
• Rule for fixing missformatted lists api.serlo.org#1682

[hugotiburtino]

We shouldn't have a bot for that, it has just to be saved correctly.
Anyways, I transfered the issues to serlo/api.serlo.org in order to make migrations for them in the future. The code for the migration can be repeated once in a year if necessary