Describe the bug

Status quo:

• The GPL preamble in About Jamulus is in English (untranslated). The newly added GPL preamble in --version output is translated. That's inconsistent.
• The way of implementing the translation is non-optimal for translators as pointed out by @BLumia in Update zh_CN app translation for 3.8.2 #2313 (comment)

To Reproduce

• Compare About Jamulus with --version
• or: Perform translations

Expected behavior

We should:

• Decide if this text should be translated at all. For context: cat --version translates it.
• If we do translate, the GUI version should be translated as well (it would be more natural for the command line version not to be translated as other command line outputs aren't translated either).
• If we wanted to show a translated version on CLI, we would have to load translations, which are currently loaded for GUI runs only.
• @BLumia suggested using a single tr ( ) call with included new lines (\n). This sounds good to me. There's also the possibility to pass comments to translators such as "Please align to X characters" (the status quo value for X is rather wide...?). The way to pass such a comment to translators seems to be to use a special //: Comment which is transferred to .ts files by lupdate.

Version of Jamulus

3.8.2_beta1

Additional context

I'm not keen on decoding this, I'm fine either way, but we should be consistent and make life easier for translators.