[Icons-Only Task Manager] Only show progress indicator for apps that are running

Summary:
Currently, Pinned Icons-Only Task Manager launchers are capable of showing progress
information even when they're not running, because the app didn't unset the progress
information before quitting, or crashed in the middle of an operation. But the concept
of an in-progress operation for an app that isn't running doesn't make logical sense.

This patch fixes that UI issue by only allowing pinned IOTM apps to show progress
information while they're actually running.

BUG: 409687
FIXED-IN: 5.17.0

Test Plan:
Pinned Elisa app no longer shows progress information on its icon after quitting while
playing a song

Pinned Discover app no longer shows progress information on its icon after crashing in
the middle of an update

IOTM apps still shows progress information while running

No change for regular Task Manager

Reviewers: #vdg, #plasma, ndavis

Reviewed By: #vdg, ndavis

Subscribers: broulik, plasma-devel

Tags: #plasma

Differential Revision: https://phabricator.kde.org/D24001