Version 0.0.37.

* Move plot's Y axis and labels with the last data to the right, so the last
  plotted value is near the axis and the labels.
* Fix the width of the plot's last value labels. It must not change with the
  value displayed in it, else it might distract the operator.
* Update Doxyfile.in.
* Fix UI not clearly showing that available data is old, see
  https://gitlab.com/mosimpa/documentation/-/issues/163
* Use the JSON proposed at
  https://gitlab.com/mosimpa/documentation/-/issues/164 in order to better
  differentiate between a missing device and one without enough battery.
* Be able to check if datakeeper is up and running, see
  https://gitlab.com/mosimpa/documentation/-/issues/166
  - Produce a sound alarm that inhibits the other alarms.