Enhancement #1360550 Shortcut to template editor
Add a new tool to easily test templates. Go to Preferences->Toolbars to add the tool to one of the calibre toolbars. Fixes #1360550 [Shortcut to template editor](https://bugs.launchpad.net/calibre/+bug/1360550)

Merge branch 'master' of https://github.com/cbhaley/calibre