Relies on slaclab/pydm#1116

Fixes a bug where the autoscroll would not be disabled after users added new axes or imported files.

• Changed which signal to listen for
  • Turns out I made some incorrect assumptions about how MultiAxisViewBoxes worked. I thought that because the changes are being propagated out to all other ViewBoxes that I can just listen to the initial ViewBox in MultiAxisPlot.
  • That was incorrect, because as we add more Y-Axes the X-Axis is linked to different ViewBoxes. This results in the signal I was listening for being emitted from a different ViewBox and going unheard.
• Change signals from clicked to toggled
  • This prevents the slot from being called hundreds of times everytime the user scrolls
  • hen the buttons are toggled the slots are just called on the first change.
• Remove the context menu from the plot
  • Remove the context menu. Caused a desync issue between the plot and the rest of the app, so I just removed it