Summary:
Extract the strings: one main catalog and a catalog for each plugin.
Also use the ECM macro to install the translations.
Ref T6858
Reviewers: #falkon, drosca
Reviewed By: #falkon, drosca
Subscribers: drosca
Tags: #falkon
Maniphest Tasks: T6858
Differential Revision: https://phabricator.kde.org/D8049
