The current energy plot does not display any time line. This patch adds a grid and time stamps to the X axis.
It is assumed that the X axis of the plot ranges from [Now - Timespan, Now].
The timestamps for the timespans greater than "1 hour" are aligned to either half hours or full hours.
The resolution respectively the divisions count or number of ticks is made dependend on the timespan.
Dates are only shown if the date changes in the timespan.
This patch may be only of temporary nature until [[ https://invent.kde.org/kde/kf5quickcharts | kf5quickcharts ]] becomes production ready.
As QML was absolutely new to me, I am looking forward to your review.