Use variable intervals for printing temperature and heart
beat labels. Obviously, so that the labels don't become
sparse on zooming, but also to make them not too crowded
on mobile / small screens.
This doesn't work for depth labels, because these labels
use data provided from the profile.c core that doesn't
know about the size of the chart.
Signed-off-by: Berthold Stoeger <bstoeger@mail.tuwien.ac.at>
efc89b9d9c