Allow uploading of images to interview transcripts

Currently, images cannot be uploaded to an interview transcript, though audio/video/documents can.

If an interviewee is discussing their particular setup or making sketches to support the discussion, the interviewer will often take photos and add them inline in the notes. Files can be added to the “Report” section but that is less helpful as it removes the images from their context in the interview.

Context is lost from the collected images, e.g. they cannot be placed/stored inline where they were relevant to the conversation.

Allow image files to be uploaded to the interview's transcript section.