Add keyboard accelerators for the normal and HTML tabs in the comments editor
Fix #1388646 [Little typo](https://bugs.launchpad.net/calibre/+bug/1388646)
Fix #1388629 [Little typo](https://bugs.launchpad.net/calibre/+bug/1388629)
Fix #1388624 [window buttons missing in GNOME 3](https://bugs.launchpad.net/calibre/+bug/1388624)
Fix e-book viewer not displaying cover from HTMLZ files. Fixes #1388595 [Cover not referenced in index.html file](https://bugs.launchpad.net/calibre/+bug/1388595)