MT#3961 Add Italian translation.

Also prepare Spanish and Russian translation files for DT.
MT#5251 Optimize billing fees upload.

Bring down upload time from 180s to 16s by optimizing purge of existing
ones (one query instead of one-by-one deletion) and optimizing upload
in batch (one query instead of one-by-one deletion).
test commit
Merge branch 'ipeshinskaya/InvoiceTemplate' of git.mgm.sipwise.com:ngcp-panel into ipeshinskaya/InvoiceTemplate
Invoices - a little bit more clean. But still DB is fake, and columns titles are interesting to think about more.