Introduce Message Formatting with Actiontext Trix Editor

[yksflip]

This introduces to possibility to send formatted messages and attachments with the messages plugin.

• fix render attachment to actually display a link to attachement
• scheduled cleanup for attachments
• max file size
  *[ ] test email reply with attachment, is it shown in foodsoft then?
  tried around a bit but still not sure what's going on there, I'd guess the message data will just be shown as a plaintext.
  I think if this is a use case we can have a look at some other point ...

[yksflip]

two questions that are open to me:

1. Any ideas for a better way in the message .html template than using this extra translations fields?
2. At the moment the db migration, javascript etc. is done globally, even though the message is a plugin. Should I try to move everything to the messages plugin or can it stay there, as Actiontext might be useful in other places e.g. the Wiki?

[yksflip]

@lentschi could you have another look at this? :) It' the first rake task I ever wrote, but I think it works as intended.

For the rake task I'd leave a note addressing the new config field in the Release Notes ...

[decentral1se]

Quick pass on this, LGTM! Thanks for working on it, definitely nice feature to have.

[paroga]

i don't know what you preferred way of working is, but if
a) you want to squash you changes during merge, the PR contains IMHO too much unrelated changes (one commit should change only as little as possible. e.g. (1) just add the trix editor, (2) adopt messaging to use trix, (3) add prune_old_attachments)
b) you want to merge it with the whole commit history, the PR contains too much useless commits like typo fixes.

since developers read code much more often than they write it, creating a clean git history should have some importance. (especially if nobody writes any kind of code documentation ;-))

[yksflip]

thanks for your review paroga!
You're right regarding the commit history. I was sloppy here and there, I'll split it into more meaningful commits and try to keep that in mind for future PR!