More y-axes

[johanfforsberg]

A request from the users is to be able to let each attribute have its own Y axis, so that they can all be scaled independently. This is very useful in order to see how lots of different things correlate in time. The epics "striptool" https://epics.anl.gov/EpicsDocumentation/ExtensionsManuals/StripTool/StripTool.html#GraphWindow that was used at the old MaxLab has been brought up as an example.

Today the viewer has only two independent Y scales, right and left and each attribute is displayed on one of them. Technically there should be no problem to support more Y axes, it's mostly a matter of UI and how to present it. Displaying many axes at the same time doesn't seem like a good idea since it becomes a mess visually. The striptool apparently only displays one Y axis at a time, depending on which attribute is selected.

I think this would require some changes in the UI but it would be a powerful feature.