Rework transcription detection

[TimJentzsch]

To search a transcription, the bot currently first tries to look for it in the comment forest of the submission. This can take a lot of API requests and seems to be unreliable sometimes. Afterwards, the bot will check the user's profile.

I propose that we immediately use the user's profile to find the transcription. This has several advantages:

• Less code to maintain (and the comment forest API is not really easy to use)
• More consistent
• Less comments to search, one API request will be enough
• If the user didn't include the footer link, but made a comment on a post, we can suggest to recheck the formatting guidelines

Of course we will have to make sure only transcriptions on the actual submission are picked up. We will also have to make sure that multi-comment transcriptions are handled correctly.