Compat with jupyter's new HTML table style
See also discussion in https://github.com/jupyterlab/jupyterlab/issues/961

With the upcoming notebook 5.0 release and in current jupyterlab, jupyter has a new (much better!) default HTML table styling. The only problem is that it fixes the width of columns hardcoded at 150 px.

IMO this is a problem. Not the default as such, but the fact that you cannot easily change this when you *want* to see long table content. The result is that when having cells/column names with long content (and sometimes you deliberately create such cells/column names), it is *impossible* to inspect those data with the default repr.
Only solutions are to inspect specifics such as `df.values` or `df.columns`.

Another consequence is that the `pd.options.display.max_colwidth` option becomes useless. 

Possible way forward:

- override the `max-width` for our html repr's to set it to 'none' (@TomAugspurger shows here that this is possible: https://github.com/jupyterlab/jupyterlab/issues/961#issuecomment-252095223)
- if we like the more narrow default, we can always decrease the default for `pd.options.display.max_colwidth` (currently 50 chars) at the same time. The the default looks similar to jupyter's one, but you have still the ability to adjust it with our options.


