Add pt_PT language

[andrepimpao]

I've added an extra line of text to the meta-title-template-help translation with the {{ site.title }} parameter info, because it is really helpful in this context and I think all other translations should have it.

I can remove it if you don't agree, for coherence with the other languages.

[tobimori]

In general, everything from the blueprint Kirby query language (https://getkirby.com/docs/guide/blueprints/query-language) can be used. This was also mentioned at that field previously.

Now, I think of KQL in the Title template as "unofficial feature", it's supported because of the {{ title }}, but I don't want to promote it, a) because there might be side effects that I don't know yet & b) it's not easy to understand for editors that don't know a sites' codebase or blueprints.

For that reason I'd remove it again.