Change icons for Activities dataengine and runner

Summary:
KCMs should have color icons while widgets should have monochrome icons, so I have changed the name of the KCM icon.

Depends on D18529

Reviewers: VDG, Plasma, ngraham

Reviewed By: VDG, ngraham

Subscribers: plasma-devel

Tags: Plasma

Differential Revision: https://phabricator.kde.org/D18532