Display inactive filesystem error on hover

[RRosio]

This PR adds an event listener based on the presence of an error class for inactive filesystems. It displays a styled tooltip with a short traceback of the error to inform the user of the filesystem status.

Still TBD:

• prevent backend requests for inactive filesystems
• resolve selecting filesystem colorization bug
  • this issue is with filesystems that are not successfully selected (although their color is changed) because of a server error, they are not properly deselected (color for selected item is not removed)

[martindurant]

Screenshot, please! :)

[RRosio]

Thanks for the comment @martindurant I just updated the top comment with the screenshots!