[kicker/kickoff] Use discover icon for manage application action
Summary: While not 100% technically correct since another app might be associated with appstream URLs it's still much more expressive than the current icon
Test Plan:
Reviewers: Plasma, hein, ngraham
Reviewed By: ngraham
Subscribers: plasma-devel
Tags: Plasma
Differential Revision: https://phabricator.kde.org/D23623