Restyling

Removed sass and did total restyling for ngWig - simplified styling a lot.

Things to do (javascript part)
* link stylesheet from inside the iframe (in <head>) once iframe is added
* add "wn-content" class to iframe's body
* add active state to editor buttons (js mostly, for design, just add "nw-button--active" class to the corresponding button)
* add linking functionality