Chain Chunker and Noun Phrase Mention Finder Addition + Immutable Span Var List + Mention Package Removal

This is a big one: 
Added Chain Chunker to parse
Added Chunk Mention Finder to parse

Added work on immutable span var list and all changes to files that once used span var list
    Note this change makes SpanVarList immutable, outside code might have to be changed

Made Noun Phrase Gender and Number labelers generic to be used for mentions and noun phrases
   I tested forward coref using the noun phrase gender and number labelers and we got identical scores
Made Mention extend from Phrase to remove duplicate code

Created mention package in coref for classes relating to the mention detection step of coreference
Removed the Mention package
   All mention related classes were moved to coref.mention including all mention detection code for coref and the mention type itself

Moved ConllCorefLoader from coref to be LoadConll2011 in load package