Caption: Bulk Editing

Design and build the bulk editing interface for captions in media. The interface should include a video player and a table of captions.

In the launch page (initial page):
- [ ] have a list of existing transcriptions, e.g.:
* per language
* per source (e.g., pulled from kaltura, processed by azure, uploaded via VTT, etc.)
- [ ] create a new transcription by uploading a WEBVTT file
* possibly modify database schema (currently 1 row = 1 transcription line)
- [ ] delete a transcription (w/ confirmation)

In the caption editing page, a user should be able to:
- [ ] edit the `begin/end timestamp` and `text` of a caption
- [ ] delete a caption
- [ ] add a new caption after/before any existing caption
- [ ] handle the timestamp carefully, ensure there's no overlapping
- [ ] set a paragraph break between two captions
- [ ] [idea] combine adjacent captions

.... more descriptions will be added.