Fix issues from D24798 comments by @davidedmundson

Summary: Lower QQC2 version to minimum requirement. Add context to i18nc function. Cannot use `i18ncp` because the number isn't integer.

Reviewers: #plasma, davidedmundson

Reviewed By: #plasma, davidedmundson

Subscribers: plasma-devel

Tags: #plasma

Differential Revision: https://phabricator.kde.org/D25319