v0.7.2

Fixes

• Opening or adding a video no longer freezes the window while it's probed — slow disks and long streamed recordings are read in the background (#32)
• Opening a new video over an edit you haven't exported now asks first instead of discarding it (#33)
• Editing shortcuts no longer act on the timeline while the help overlay is open (#34)
• Thumbnail extractions that are cancelled or get stuck are killed instead of piling up (#35)
• If the file dialog never answers, pressing Open again brings up a fresh one instead of doing nothing (#36)