js: Fixed "L is undefined" errors

D'oh!
css: Added OpenLayers 3 styling support and example
css: Split SASS file into multiple files

Let's use one file for each mapping framework
css: Removed ol3/leaflet-sidebar classes

Those are not necessary anymore, now that we use CSS files per framework
css: Removed duplicate $sidebar-margins definition in ol3 styling
css: Removed duplicate color definitions in ol3 styling
css: Renamed sidebar.scss to _base.scss
css/ol3: Implemented half-transparent sidebar in XS mode