Fixed packaging and headers for the generated Mix10 lib files
Merge branch 'develop' of github.com:Sable/mclab into javascript-backend
Some refactoring:

- Renamed JSFixVars to JSAddVarDecls
- Renamed JSFixBuiltins to JSRenameBuiltins
- Moved the above two classes to the
  natlab.backend.javascript.transformers package
- Added apply() method to JSAddVarDecls to modify the Function node.