Country restrictions - increase maxlength

I decided to open another issue instead of re-opening: #1532182: Country restriction.

Attached is a patch that increases the maxlength of the country restriction textfield. This is necessary for implementing a long list of countries, like all the EU countries (which btw, I think should somehow be included to allow a single "EU", instead of having to manually list all of them individually):

Austria, Belgium, Bulgaria, Cyprus, Czech Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Poland, Portugal, Romania, Slovakia, Slovenia, Spain, Sweden, United Kingdom