[SMS App] Fix sending simple SMS
Summary
In !316 (merged) we made some changes which are not backwards-compatible with the Android app. Since we have not yet released the Android app since those changes, we have hopefully not broken anybody but me.
However, this might be related to a recent bug: https://bugs.kde.org/show_bug.cgi?id=425638
Also updates some of the header comments for the recent changes
Test Plan
Before:
The Android app will throw an IllegalArgumentException
After:
With this plus kdeconnect-android!207 (merged), plain-text SMS can be sent again
Edited by Simon Redman