Refactoring code for interactive tools where possible

[JorgeGtz]

We have talked about how the new point annotation tool #816 could be useful in several functions (custom roi, 2d segmentation, etc).

I think we could modify most of the interactive tools to be based on the point annotation and reduce the code repetition.
Among the current PR we have:

• Annotation sub-package and point annotation tool (a.k.a. interactive CustomROI)  #816 Could be the base.
• Add img registration #729 Collects points on two images displayed at the same time. This could be handled by generalizing the point annotation to work with multiple instances of Axes and return a list of lists of points.
• Interactive object count #754 Collects points with different 'labels' as a dictionary. The structure of the function is a little different, but I think the most important functionality is that it can 'import' an independently generated list of points.
• Visualize show spectra #723 Has a slider bar and the joint plot updates with each click. This might need to be self-contained.

[HaleySchuhl]

Generalize the point collection tool. There are different methods downstream that should be supported by this base function. Need to be able to handle a flexible number of axes, some downstream tools just take in a list of points, image registration registration requires two lists of points... so we need to consider each potential use.

Seems like modularity of functions would be wise. In any case where the process is fixed (the downstream step is constant) then tools should be combined to reduce the complexity of workflows for users. Utilize wrappers for common multi-step processes!!

Keep consideration for tools that could translate into parallel analyses and how to enable this.

Brain storm on how vertex collection can translate into Naive Bayes training dataset building.

When it comes to vertex collection where a small region around with a variable radius, seems like having that radius as an adjustable parameter would be more practically useful compared to an interactive slider.

Note for myself re #816 move the class into the classes.py file since it will be used by multiple sub-packages.