Draw ROI

[roaldarbol]

Add a function where the user can input an image or video (from which a frame is drawn), and interactively draw a ROI (or more?). Use a Shiny app to do this; Shiny is then added as a Suggests package. Probably using magick/av for the functionality.

Really needs to figure out how we'll be handling ROIs and spatial features (distances to stuff, time in zone, etc.) to figure out how the ROI should be output.