Compare attributions and signals

[mstykow]

Is your feature request related to a problem? Please describe.
In #2488 we introduced the ability for the user to compare an attribution with its original signal, if it exists. In this story we want to extend the functionality to also compare a selected attribution with any other attribution or signal. This can be useful for comparing similar attributions, for example.

Describe the solution you'd like
Integrate the diff view into the regular audit view which contains the list of attributions and signals.
Possibly hide the resource browser while in diff view to make more room.
Freeze the selected attribution in the right pane and allow the user to select any attribution or signal from the lists to display in the left pane.
Rename button "Compare to original" to just "Compare". When clicked on initially, display the original signal, if it exists.

[mstykow]

Duplicate of #2563