Add i18n and Italian translation

I18n, Italian translation of jinja templates and English translation
of remaining messages printed to terminal.
At the moment only it_IT is used, see launch_script.py, line 275.
Create only requested web pages
Add file to .gitignore:
data/wikipedia/wikipedia_it_coordinates.csv
Fix bug: the program should stop if poly file is missing

Reported by Cristian Consonni
Add jinja2 and babel to requirements