Allow retrieving a specific program from a Project

Also change MatlabProgram.getPath() to return a java.nio.Path instead
of a String.
Add MatlabProgram helper that creates Project.
Add a transformer to RefactoringContext.
Eliminate some duplication in McLint tests.
Fix bug in MatlabProgram.at.
Add MatlabProgram.getAbsolutePath()
Eliminate duplication in pretty printer.