Added Dutch translation

[Vistaus]

🙂

[gustavo-iniguez-goya]

Thank you @Vistaus !!

Could you leave out of the PR all the files except ui/i18n/opensnitch_i18n.pro and ui/i18n/locales/nl_NL/opensnitch-nl_NL.ts ?

The other translations and the files *.qm don't need to be updated.

By the way, if you use weblate most of the translators use it to translate the GUI: https://hosted.weblate.org/projects/opensnitch/gui-main-branch

[Vistaus]

Oh, it automatically updated all those files when creating the Dutch file. But I've just uploaded the file to Weblate!