Support loading pandas DataFrame's from pandas.HDFStore

[yarikoptic]

e.g.

In [6]: import pandas
In [7]: df = pandas.HDFStore('/tmp/d.h5')
In [8]: df
Out[8]: 
<class 'pandas.io.pytables.HDFStore'>
File path: /tmp/d.h5
/d            frame        (shape->[2,14])

In [9]: df['d']
Out[9]: 
                      condition        RT pgender  dirty  bindex  btrial dir  subject       trial                                                            
...

[ChrisBeaumont]

Adding new data loaders to https://github.com/glue-viz/glue/blob/master/glue/core/data_factories.py is actually fairly straightforward and documented at http://www.glueviz.org/en/latest/customization.html#custom-data-loaders ... any chance you interested in putting together a PR?