DataStorer attempts to import HTML file

[rufuspollock]

Given this link the DataStorer will attempt to import this to the DataStore even though it is HTML: https://github.com/pudo/lobbytransparency/master/etl/countrycodes.csv

This can lead to severe problems when the data viewer loads (in fact crashed my browser) probably because of either huge number of columns or weird html.

Interesting question as to what we should do? Should we not import stuff with mimetype text/html or should we check actual content (often case things are not sent with right mimetype).