Added the 'CurrentSymbol' property to LrItem, and used it to simplify a few places in the code where we were manually getting the next symbol from the production rule.
Removed the ParserStateIds field from LrTableGenEnvironment -- it was redundant since we're already using a TagBimap within LrTableGenState.
Minor code cleanup.
Shorten test timeout to 30 seconds. Eventually it should be shortened down to 10-15 seconds.