Clean up assets#edit UI and add Licenses

[sudara]

Track Edit was never designed in Figma, it was always a hodge podge. Attempted to bring things in line with other forms, etc:

Notes:

• If there's no license I would like the text to say "Add License" vs. "Edit License" (a lot of people won't have any idea about what licenses and I don't want to confuse before the user took action)
• The orange license short codes link out to the license on CC's site. These links should be underlined, like the other orange links on the site.
• "Re-Upload song" header should actually be "Upload New Version"
• "Upload New Version" will need a "Choose file" button. We didn't style this, but it can be a left aligned gray button (ala change license).