Workaround for Qt 5 regression that prevented the keyboard shortcuts for the various Similar books actions from working
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
Small improvement on template tester messages.
Enhancement #1360766: show plugboards for disabled devices and allow entering plugboards when no metadata writer is enabled.