Restore snapshot improvements

[Poul Bak]

1. When double clicking a snapshot, this should mean: Restore this snapshot.

Similar to (but easier than) clicking on the snapshot and select the restore button.

2. When current state hasn't changed and you restore the nearest snapshot, there's no need to display the confirmation dialog. Nothing gets deleted and the operation is totally reversible (simply by restoring the previous snapshot again).

3. The message that comes up, when you restore a snapshot and current has changed only asks if you want to create a snapshot of current state, but not why I would want that/what happens if I do.

The text should clarify that I can create a branched snapshot tree, something like: '...... by checking the checkbox below to create a branched snapshot tree; if you don't....'

4. That checkbox should be OFF by default! Normally when restoring a snapshot, you really want to delete the current state.

5. Documentation shows an image with branched snapshots, but not a word about how you create a branched snapshot tree. Please add some text about that.