ENH: Add version as attribute of Table

fixes#510 

Version should be an attribute of the table.  On init it currently defaults to (2,1) for future releases it only needs to be changed in one place now. 
@ElDeveloper, is there a way to get the SHA of the commit, in the case that it's dev?  If so, that would be excellent to include here, too!  I think I have seen an example of this when I execute ```print_qiime_config.py```