Workaround broken file chooser dialog on Ubuntu that does not auto-insert the specified extension. Fixes #1275125 [Edit book: cannot create new empty book when extension is not specified in the file](https://bugs.launchpad.net/calibre/+bug/1275125)
Commit dirty editors to container before creating a checkpoint so that you dont lose any WIP when reverting to that checkpoint later. Fixes #1275097 [Edit Book: Create Checkpoint possibly lacks a self.commit_all_editors_to_container](https://bugs.launchpad.net/calibre/+bug/1275097)
Nicer names for checkpoints and checkpoint actions
Edit book: Auto add a checkpoint when the book is first opened for editing