Migrate deploy configuration to Capistrano v3.
Update license badge

Because blue is more beautiful :)
Clean code

Fix issues recovered by scrutinizer-ci.
See https://scrutinizer-ci.com/g/openl10n/openl10n/inspections/ecf7a92c-beea-4789-945a-e0912b5f5346/issues/?status=existing
[Project] Add the description field