Use information from the jsTree instance to populate showWell

With certain changes in the show infrastructure it is now possible that
the (a) "show" query string variable cannot be shoved off to the
delegate template without context and (b) that it will not have been
fully resolved by the Python stack.

We are guaranteed that the initial settings of the jsTree instance have
a fully resolved, and validated, set of instances.  This commit makes
use of them.
Fix typo
Ensure that less garbage ends up exposed on load failure
Strip needless white space
Make Well lookups work in a much larger set of cases
Add an extra Well to fixtures for testing other conditions
Expand test to cover the Well in a Plate without WellSamples case

Currently we only resolve the Plate in cases where the Well is in a
Plate but has no WellSample associated.  It should be possible to
perform this lookup by examining the PlateAcquisition's linked to
the Plate and selecting it if there is only one linked.
Remove unneeded Well retrieval
Try harder to find the PlateAcquisition
Update some documentation