Use KDE's translation facilities for svnqt
Right now the strings in svnqt that use QCoreApplication::translate
aren't picked up by Scripty, so they end up not being able to be translated in KDE's translation infrastructure. This MR makes them use i18n from KLocalizedString instead, which should mitigate this.
Since src/svnqt already depends on KF5::ConfigCore anyways, it should be fine to also depend on KF5::I18n. These changes should then be picked up by Scripty like other translated strings.