Add ability to specify level prototype as a name (close #367, BEM-949)
Proper error message when first level in the inheritance tree is not found
Code style and remove redundant PATH.resolve()
baseLevelName has higher priority than baseLevelPath (when first is specified the second is ignored)
Merge pull request #435 from bem/BEM-949

Add ability to specify level prototype as a name (close #367, BEM-949)