Support Array Plots

[beetleskin]

Thanks for the great plugin, it makes my everyday ROS life much easier :)

However, I'm often faced with plotting arrays as such, not over time, and there is no single plotter out there capable of this. So this might be a nice feature to add here.

I'd fancy a plotter, that can handle array types, e.g. float32[] data-fields. The x-axis would be the index of the element, y-axis the value of the element. The whole plot would refresh with every new message.

Additionally nice to have:

• keep a history of past plots and fade them over time
• support arrays of custom data types by selecting the element to be plotted
  • e.g. think an array of PoseWithCovariance[] pose_list
  • then the user could select pose.pose.position.x
• support multiple data-series per plot
  • by selecting multiple elements
• custom x-axis
  • in the pose example, plot e.g. pose.pose.position.y over pose.pose.position.x for each pose in the array