Added bg color controls

[BraydenThompson]

Closes #101

Discussion

Hooked in functionality of color picker widget into the ipyvolume graph. After researching how to change the transfer function colors on the volume graph, I found that there is no natively supported way to change the colors in Ipyvolume. In their repository, there are attempts to implement improved transfer functions. See: here, here and here, but they seemingly haven't gone anywhere.

A recommended solution here involves modifying the rgba image output of the graph, and rendering that to screen, which seems like overkill for this task.

Overall, it seems unlikely that we can change the colors without modifying ipyvolume's code to some extent, which is a larger discussion we will have at our next meeting.

Testing

• Run build.sh and make sure new dependencies install in .venv
• Open up the notebook (make sure using the .venv Python kernel)
• Execute the cells, update the color in the color picker, and re-run the display cell, making sure the background color updates.

[matthew-oberg]

Tested locally and working.