shepherd should signal back grabber/component failure to a central source

[lincoln]

While one of Shepherd's primary design goals is to handle failure of individual components, keeping track of what components are are "working" versus those that have "broken" will be a challenge.

When shepherd checks for updates, it should optionally signal whether it has seen any grabber/component or data failures. Shepherd developers can then use this as a hint as to whether something has broken or not.

The sending of (anonymous) data should be able to be disabled by the user.