[Comics & Weather widgets] give "Configure..." buttons icons

Summary:
This patch gives the Comics and Weather widgets appropriate icons for their {nav Configure...} buttons.

BUG: 399888
FIXED-IN: 5.14.2

Test Plan:
{F6335981}
(Weather on top, Comics on bottom)

Note that the size discrepancy appears to be an unrelated `PlasmaComponents3` bug: https://bugs.kde.org/show_bug.cgi?id=399952 (The Weather widget uses PC3, while the Comics widget uses PC2)

Reviewers: #plasma, kossebau, davidedmundson

Reviewed By: #plasma, davidedmundson

Subscribers: mart, plasma-devel

Tags: #plasma

Differential Revision: https://phabricator.kde.org/D16287