Allow translators to use Automatic translation

Automatic translation in weblate translates strings that have been already translated in other components.

This is very useful specially on common titles or XML tags. I have been translating automatically for a while, for example when there is a new release all the titles for the post get translated in most of our languages (except 'Tails x.x is out', because the number for the release changes, so it does not get automatically translated, although the suggestion appears on the Machine translation tab for translators to copy and edit).

I think it would be interesting for translators (not reviewers, but plain translators) to have the posibility of doing such automatic translation, as this will prevent wasting their time on repetitive translations and prevent inconsistencies.