Add Initial GUI

[jeffstjean]

Pretty extensive changes to get tkinter working. I had to off-load all the algo still to a child thread since Tkinter needs to run in the main thread.

This is just an initial pass at the GUI but it has a lot of the infrastructure to build off of for smaller, easier to review changes in the future.

All messaging between threads is done using queues. The Application has a queue for inbound messages (eg. telemetry, images) and a queue for outbound messages (eg. if the user changes parameters and presses save) so we can pass messages back to the algorithm. All messages are passed using the types defined in Messages.

It still needs some cleanup and better typing but wanted to share as a proof of concept.

Some future TODOs:

1. Add markers for each detected centroid by passing a Point (one for each colour)
2. Figure out why the image has some weird padding around it (that's why it's really small)
3. Handle algorithm parameter changes (eg. updating the threshold arguments)
4. Add interface for selecting the target landing zone (by clicking on the marker)
5. Add polygons around each detected cluster (once Cluster algo is done)

[jeffstjean]

This is probably going to have conflicts with #16. We'll merge yours first and then I'll resolve conflicts.