applets: use appropriate case for title/description

Reason for the change

The HIG recommend sentence case for subtitles, which is how applet descriptions are commonly displayed, while applet names fall under the rules for title case. Some applets use title case in description or sentence case in their name.

This commit makes these applets use appropriate capitalization.

Test plan

New capitalization was checked with Widget Explorer.

Screenshots or screen recordings

(before screenshot only shows an example, after screenshot shows all cases)

Before	After

Bugs fixed

N/A

Note

The descriptions could use a general rework for consistency with each other, but we should develop general guidelines for this (and plugins in e.g. KDE Connect or Kate), and with string freeze coming up this is probably 6.3 material.