Fix localization of the systemmonitor widget configuration window

Summary:
Currently, the common config window messages are neither extracted nor used in all 5 widgets. It is not possible to add several translation catalogs for a single QML widget thus the messages are extracted into all 5 widget catalogs.

Idea of the fix by Victor Ryzhykh.

Test Plan: Extraction tested to work as expected, translation should work too.

Reviewers: #localization, #plasma, davidedmundson, ngraham

Reviewed By: #plasma, davidedmundson, ngraham

Subscribers: plasma-devel

Tags: #plasma

Differential Revision: https://phabricator.kde.org/D26192