Add visualizer

[TimMagoun]

• Use TonioViz as trajectory, landmark, and range visualizer
• Added example and example dataset.
• Depends on TonioViz PR#22 1d103de6

[TimMagoun]

TODO: Add docs to readme, add instructions about installing opencv and pangolin (v0.6) which TonioViz depends on

[alanpapalia]

In the CMakeLists.txt I set viz to default to on:

set(ENABLE_VISUALIZATION ON CACHE BOOL "Enable visualization module.")

This is to make sure that we have the build environment nailed down to perform visualization. If it's a pain to modify the build environments in the github actions then I'm okay turning it off by default and letting interested users follow the instructions to set it up.

[TimMagoun]

LGTM!