Tooltip: Show full selector path. (#371)

Fixes #371. Works fine for LESS.

For SCSS, even the [hacky solution](https://github.com/am11/WebEssentials2013/commit/4f0ab10309d240a7274d94d486f9101a4b11f4c2) doesn't guarantee if all selectors would be mapped to the source (eventually we need to match the selector name which bring us back to square 1: the reason we chose source-map over our manual LessDocument/ScssDocument approach). 

FWIW, its the issues with libsass, (the backbone of node-sass, which we are using). However, the original [sass gem](https://github.com/nex3/sass) generates correct source maps. See https://github.com/hcatlin/libsass/issues/324#issuecomment-39074495.

@madskristensen, this PR is isolated from the previous one (its coming from separate branch). I have made changes in (two) separate files. It can be merged for v2 without breaking anything. :checkered_flag: