wide table support
addresses #6245 

@jreback this isn't quite working yet for older arrays - the reason is because I have to address values_block_kind_0 and things like that.  Currently what I'm doing is creating a group under `self.group` of the Table class, named 'attr', which has all the attributes as CArrays.  However the issue is that values_block_kind_0 is actually written as an attr of the table dataset, not the group.  I can definitely setup the code to read that stuff for backwards compatability, but is it ok if I put all carray attrs as datasets under the attr group, or is there some namespace collisioning that I'm not aware of?
