Renders the dump creation modal. The first panel takes a link, previewed through GET /api/remote/preview and checked against GET /api/dumps?url=, or a file. The second takes the "why", categories and visibility, and posts to POST /api/dumps. The third adds the new dump to playlists. The new dump is handed to WSContext's injectDump so the feeds show it at once. Everything but the file is saved as a draft (utils/dump/draft.ts) until it is posted.