[dict] Modernize configuration window

Summary:
This patch bumps dictionary's settings QtQuickControls from version 1 to 2.

It also changes the configuration category's icon to match the applet's one.

NOTE: It would be good if we could get keyboard navigation to work, it doesn't seem to want to be doing it now.

Test Plan:
Before:
{F6791492}

After:
{F6816990}

Reviewers: dfaure, ngraham, #vdg, #plasma, davidedmundson, mart

Reviewed By: ngraham, #vdg, #plasma, davidedmundson, mart

Subscribers: GB_2, mart, broulik, plasma-devel

Tags: #plasma

Maniphest Tasks: T10586

Differential Revision: https://phabricator.kde.org/D20797