Assets function and fixes

2 quick fixes:

1) Use the Twig `asset` function for the `baseUrl` - I don't know why I thought having a CDN path for this would mess things up, but it appears to be fine. See sha: fe37dc1e8e198f73869052a817b9cab9a998d3d5

2) Fixed the `grunt default` task, which was deleting the copied sass files before they were being used. This may be not be needed later anyways, after #3