Verify that all strings are properly escaped (#5558)

Verify that all strings are properly escaped (#5558)

- I checked every occurence of a '%2' and make correct use of the
QString::arg overload that takes several argument instead of chaining
them, because the first argument can contains a '%1'

 - I tried to look for every label that they either use plain text or richtext
and escape the user provided strings in there.