Translate unit names & fix external signer error

[luke-jr]

I think I got everything under src/qt missing translatability.

Exceptions:

• Punctuation-only (this is a can of worms)
• Date/time (long-standing ignoring of locale, not sure anyone minds)
• Obscure errors
• Technical terms in transactiondesc

Notably, I did include units. Not only for the benefit of non-Latin languages, but also we have "bits" and "sats" nowadays that likely make sense to translate even in Latin-based languages.

(Much of this was merged in #724 already)

[hebasto]

Concept ACK.

[katesalazar]

great idea

[DrahtBot]

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Conflicts

No conflicts as of last run.

[luke-jr]

Rebased (no changes, just had to re-generate the make translate outputs)

[DrahtBot]

🐙 This pull request conflicts with the target branch and needs rebase.

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