Add Transfer/disk/deserialization info on Task Group visualization.

[ncclementi]

Opening a discussion to gather opinions to open a PR.

Currently, the progress bar and the background of the box on the Task Group dashboard visualization have as color the "random" color of the task prefix assigned by color_of. This color even though it matches the task prefix color on the progress bars, it doesn't give us much information.

After exchanging some opinions with @ian-r-rose we thought of adding somehow the color that corresponds to the max of the durations spent on transfer (red), deserialize (grey), disk read/write (orange), computation (white or prefix color).

Proposal:

• Integrate into the current TaskGroup Graph visualization the colors for transfer (red), deserialize (grey), disk read/write (orange), and computation (white or prefix color).
• The color to assign is the corresponding to the maximum of the duration spent on transfer, disk, computation deserializing. Each duration info lives in the dict tg.all_durations

Open questions/Ideas:

• Do we make this color change as the computation goes, or plot at the end?
• Should the progress bar have this new color or be somewhere else?
• I think that having the prefix color to be the background of the box when the TG is in memory should remain this way since it is informative. But then how should the transfer/disk/deserialize color info be displayed?
• One option is to use a color background on the hover.
• As an extra, encode into the visuals when we have erred tasks (currently only in the hover)