Port the dict applet to KF5 and QtQuick 2

Summary:
My wife was missing this applet, after migrating to Plasma 5.
Therefore I had to learn how to write QML-based plasma applets :-)

Test Plan:

• Adding dict applet to desktop, works.
• Looking up definitions, work.
• Clicking on a link, works.
• Hi-dpi support, works.
• Configuration dialog to choose dictionary: done in a followup commit.

Reviewers: Plasma, davidedmundson

Reviewed By: Plasma, davidedmundson

Subscribers: ngraham, anthonyfieroni, broulik, davidedmundson, plasma-devel, Plasma

Tags: Plasma

Differential Revision: https://phabricator.kde.org/D8421