This basically reverts commit 86b31dc12b.
It now works like this: If the use has pycountry installed, it is used.
If not, Dosage falls back to a small internal list generated from
pycountry by scripts/mklanguages.py.
This means additional work if we ever decide to translate Dosage, since
pycountry already has all the translations for language names...
This fixes#23.
