srv-less: Implements new (v2) API

* Fixes breaking changes for lessc.
* Explicitly remove .tscache on PreBuild.
* Fixes ServerBase and derived types.
* Renames libsass binding folder.
* Code formatting.

.. and code analysis warning fixes.

Fixes at least two issue: https://github.com/madskristensen/WebEssentials2013/issues/1664 and https://github.com/madskristensen/WebEssentials2013/issues/1665.

Note: Code Analysis warning count with Debug configuration is zero. Would be nice if we keep it that way. :+1: