Harmonize country conversion

[davide-f]

While dealing with Tanzania modelling, we realized that country harmonization shall be improved. In the GEO database Tanzania is named "United Republic of Tanzania", which leads to conflicts. We may provide a fix for that.

Moreover, when checking the dependencies both pycountry and country_converter are used, which is redundant. The latter seems more capable to handle alternative naming conventions and may be recommended

[pz-max]

Same issue here for [TW] Taiwan... TAIWAN, PROVINCE OF CHINA