When there are more than 2 countries, just list "n countries"

Users were having problems when they looked up things like "English"
and were presented with "United Arab Emirates" and such, as these
colonial languages are spoken in so many countries.
So this just displays the number of countries.
Merge branch 'MajorLanguageCountryListing' of https://github.com/sillsdev/libpalaso into MajorLanguageCountryListing

Conflicts:
	PalasoUIWindowsForms.Tests/WritingSystems/LookupIsoCodeModelTests.cs
	PalasoUIWindowsForms/WritingSystems/LookupISOCodeModel.cs