Windows support, offline/conflict resolution improvements, reserved filenames

This is for testing purpose only.
Do not install it, unless you know what you're doing.

Improvements for all platforms:

• Restoring a folder from the Cozy trash is now supported.
• We fixed some conflict resolution issues. Creating / changing / restoring
  files with the same name should be more reliable now. Some issues remain,
  though.
• Most offline actions should work now, except for deletions.

Improvements for Windows users:

• A release! Getting a code signing certificate took more time than expected,
  though, so the app is not signed yet. This should be fixed in the next one.
• Windows file/dir paths are now supported, making the synchronization usable,
  hence the release.
• Files and folders with reserved name, reserved characters or terminating
  characters will not be synchronized locally and user will be warned.

Improvements for macOS users:

• The dock icon is now hidden when closing the Cozy Desktop window, so you
  don't see it with cmd-tab when running in background
• Files and folders with colon in their name will not be synchronized locally
  and user will be warned of this character as being reserved on macOS