Handle translations

[libremente]

Translations from English to (at least) Italian must be handled.
This means that we should define a clear workflow.
Personally I think we should not use Transifex at this stage, however let's discuss about it.

[libremente]

Please check https://github.com/open-education-polito/fare-invenio/blob/master/.tx/config that explains everything.
I'd like you to try a possible italian configuration and see the results, thanks

[EugenioCorso]

I tried putting BABEL_DEFAULT_LOCALE = 'it' in /fare/config.py, but, for what i saw, only a word in the administration page changed although most of the site is translated

[EugenioCorso]

Update: not all (i.e. most of) message catalogs have the compiled file .mo file, e.g. the .mo file is missing in Invenio-accounts pypi distribution and that's a bug. It should be due to fuzzy being included in the messages.po file. Here the relative issue