In-place edition of transcription from the sidebar

Followup of #901 (closed)

We want to deprecate the transcription modal, so we need to be able to edit transcription from their display in the sidebar.

The UI workflow would be the same than in the modal:

• a user clicks on an edit button in the actions list of each transcription
• that button is only available for manual transcriptions
• the displayed blockquote becomes a textarea, with a button to submit the changes