KCM: fix QML errors, improve QML code style, use more standard components, small redesign

Nate Grahamrequested to merge
work/ngraham/polishing-and-fixing into master

It started innocently enough as a few obvious bugfixes, then came the code style improvements. Before long UI polishing emerged, and from that point on it was only a matter of time before the redesign happened!

Changes are split up into atomic commits.

Before After
Before After
Edited by Nate Graham

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