Log Browser: place zero at same place regardless of units

It would be nice if the zero point could be kept at the same place even when graphing values of different units. I find it hard to read a graph well when they're not aligned at zero. A difference in scale I can understand but zero being offset makes it hard to understand.

Start at the Mission Planner Log Browser graphing entry point and reproduce the shown case with values in different units. Compare the plotted zero positions and consider the issue complete when zero remains aligned while the differing scales remain readable.

Written by the indexing model from the issue text.