Add renderer plugin loader
Summary:
With this it's now possible to implement the diff highlighter using the
new API. However, it's far from convenient still as we can't easily
re-use Grantlee template fragments for the attachment containers yet.
Reviewers: knauss
Reviewed By: knauss
Subscribers: KDE PIM
Tags: KDE PIM
Differential Revision: https://phabricator.kde.org/D8114