Added theme.json with screenSize property

This contains small, medium, and large breakpoints to handle rendering on
different devices or changes to the viewport size.
Merge branch 'develop' into Feature/9137

* develop:
  Revert "Merge branch 'develop' of https://github.com/zenduo/adapt-contrib-boxmenu into zenduo-develop"
  Revert "Merge branch 'develop' of https://github.com/adaptlearning/adapt-contrib-vanilla into develop"
  Revert to trunk version
  Spacing for items on mobile & responsive fixes
  Updated padding issue
  Mobile support and float fix
  Updated boxMenu render of main views
  Pushed develop into master
  Updated .bowerrc file
  Updated menu styling, templates and JS
  Initial commit