Release v4.0.1

Small patch release to tidy up a couple of issues in the v4.0.0 Release.

Fixes:

• Desktop/Electron client failed to validate the URL properly on the preferences screen
• Linux Desktop app (AppImage) was missing

New Feature:

• Keyboard shortcut on image page - press space to toggle the image in/out of the basket

Docker: docker pull webreaper/damselfly:4.0.1