[applet] Make details text fully opaque and normal style

Summary:
There isn't any need to make the labels bold and all the text almost half transparent.
The view is just fine without them, and the current style is quite low-contrast with a
dark theme.

BUG: 414993
FIXED-IN: 5.18.0

Test Plan:

Reviewers: VDG, jgrulich, ndavis

Reviewed By: VDG, jgrulich, ndavis

Subscribers: ndavis, broulik, plasma-devel

Tags: Plasma

Differential Revision: https://phabricator.kde.org/D25970