Re-organise some core files to align with plugin structure

[oliverfoster]

Subject of the enhancement

src/index.html > src/core/required/index.html
src/core/js/scriptLoader.js > src/core/required/adapt/js/scriptLoader.js
src/core/js/libraries/ > src/core/libraries/

index.html and scriptLoader.js currently have their own copy entries in the grunt tasks. The can leverage the required folder pattern. The libraries folder shouldn't live in js/libraries and should instead mirror the plugin structure of pluginName/libraries as a sibling of the js folder.