Backwards compatible fix for #27

[foosel]

Moved format method into view model - no need to clutter the global namespace (and if so starting with 1.3.6 that needs to be done explicitly, see http://octoprint.org/blog/2017/12/01/heads-up-plugin-authors/)

I also adjusted the version so all you, @imrahil, should need to do here is merge this and tag a new release, and you should be set.

Closes #27

[imrahil]

You're awesome! Thank you very much!