LESS and MarginBase Fixes

* LESS: Incorrect method nesting.
* Margin: Minified file to use correct path.
* MarginBase code refactoring.
*  Helpers: Handled edge case. When target file is outside project directory, `ProjectItems.AddFromFile( .. )` throws `COMException: "Webs do not support linked files."` For instance, it will throw exception if custom folder in compiler is set to absolute or relative path, which yields a location outside the project scope.