Embed less sourcemaps with correct filepath

[baaygun]

outputSourceFiles embeds the files into the sourcemap, but sourceMapRootpath actually tells it where to find the real files by going from www/build to www

[baaygun]

This doesn't correctly work due to us using import (multiple) less directive. All the files but main and reset.less get imported multiple times with different color_stop class names, which causes source maps to fail and map everything to main.less.

I think as a step forward, this is ok to merge, and makes the problem more visible where I hope someone with more less skills can solve.

[designedbyscience]

Makes sense to me to merge