[WIP] Adding bounding boxes and fixing notebooks

[kmader]

• fixing notebook zoom code
• adding code to manipulate bounding boxes in cornerstone
• works on easy functions for ROIs #8

[codecov-io]

Codecov Report

Merging #25 into master will increase coverage by 1.6%.
The diff coverage is 92.59%.

@@            Coverage Diff            @@
##           master      #25     +/-   ##
=========================================
+ Coverage   63.28%   64.88%   +1.6%     
=========================================
  Files           4        4             
  Lines         463      487     +24     
=========================================
+ Hits          293      316     +23     
- Misses        170      171      +1

Impacted Files	Coverage Δ
cornerstone_widget/utils.py	96.77% <100%> (+0.69%)	⬆️
cornerstone_widget/cs_widget.py	90.07% <86.66%> (+0.22%)	⬆️
cornerstone_widget/_version.py	44.4% <0%> (ø)	⬆️

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[kmader]

@betatim I've added the basic functionality, but the bounding boxes do not show up for some reason. The demo.ipynb is probably the best starting point for experimenting

[kmader]

@betatim now the bounding boxes show up, but it is still a bit finicky

[betatim]

why the two tool states?

[kmader]

so this isn't a very elegant approach, but one is for setting the state (_in) from Python and one is for reading the state (_out) from Cornerstone. The state itself isn't a traitlet and the traitlet is only updated on a mouseup event