Implement a parser to extract PVS subtype expressions from variable types.

In order to support PVS style subtype expressions, the system has to be able
to parser such expressions.  To simplify the variable list parse, it simply
extracts the PVS expressions as a single token, unprocessed.  While requiring
more parsing work for the subtype expression, it avoids the necessity of
changing the parser in the future should a new subtype language be used.

As part of this change, the variable list parser's lexer became to complicated
to be expressed in Antlr's combined grammar format.  Thus split it out.
Everything works the same as before from an API point of view.

git-svn-id: https://groke.mcmaster.ca/svn/grad/colin/branches/TableTool_javization@10852 57e6efec-57d4-0310-aeb1-a6c144bb1a8b