Improve up/down display for Monitor widgets

Summary: This patch improves the up/down display for the Monitor widgets

Test Plan:
Before, no activity: {F6549441}

After, no activity: {F6550787}

Before, some activity: {F6549443}

After, some activity: {F6550788}

All the other ones still look good or are improved: {F6550789}

Reviewers: #plasma, #vdg

Subscribers: abetts, davidedmundson, plasma-devel

Tags: #plasma

Differential Revision: https://phabricator.kde.org/D18255