Image Analysis Node

The existing `ImageDisplay` allows the creation of ROIs but doesn't give anything beyond their corner points. I'm working on a new node, `ImageAnalyze`, that uses the `pyqtgraph` library. So far I've been able to allow for the user to:
- Select from different ROI shapes
- View a plot of the average in the ROI (for a stack of 2D images)
- Access that 1D data series outside the node

So far this is very much a work in progress and it may make more sense in the end to combine it with `ImageDisplay`. I'd initially started with the pyqtgraph `ImageViewer` widget, but wasn't able to change the ROI shape without crashing it.

@aganders3 it would be great if you get a chance to give this a quick test, or just help brainstorm any thoughts on what else might be useful here. If you want to test it, you'll have to set up a conda env with pyqtgraph installed. One question I'm thinking of already is how best to handle cases where someone wants a multi-point ROI and doesn't know the number of points a priori.

There are also some menu options that `pyqtgraph` has accessed by a right click that are being stepped on by gpi's in port / out port prompt — is there any way we can bypass that for a particular widget?