WIP: optional: translate twitter to mastodon mentions

[rriemann]

note that only twitter mentions of accounts registered on this crossposter instance are translated

[renatolond]

You also need to commit the changes to the schema file, that's why the tests are failing here :)

[rriemann]

I guess the schema file is updated upon rake db:migration. The problem is, that this command files, because I do not have a proper developing environment. I have neither postgres nor redis running on my PC yet. :see_no_evil: I may spin up a cloud server for dev to keep my local machine clean from dev dependencies…