Editable export: let the person fix small things themselves

This is editable-export 0.3.9.

Here is the result. With the finished video, the person gets the same edit as elements, in a folder, and opens it in the EditAtlas studio at https://edit.trysometh.ing/studio. The studio shows the video, a timeline and a panel. They can:

• nudge a sound by a frame, or turn it down
• drag a caption up
• make every caption bigger at once
• fix a typo
• trim a clip
• press Export MP4

The MP4 is made in their browser, by the same page and the same drawing code that made the video you delivered. So what they see is what they get.

Five things stay true the whole way through: