Examples for testing improved support of NWB Widgets in NWBE

As discussed with @tarelli @bendichter @filippomc, we should investigate better ways to support NWB Widgets interactive elements, especially for NWB datatypes not (yet) well supported by NWBE.
An example of this is included in these datasets:
https://github.com/OpenSourceBrain/NWBShowcase/blob/master/ScholzEtAl2018/Testing.ipynb
e.g. http://nwbexplorer.opensourcebrain.org/nwbfile=https://github.com/OpenSourceBrain/NWBShowcase/raw/master/ScholzEtAl2018/ScholzEtAl2018.AML18_moving.BrainScanner20160506_155051.nwb

The 2D Position/Spatial Series shows up as a TimeSeries plot of just the x position in NWBE:

but is well rendered as a 2D plot in NWB Widgets (after typing show() and finding the datatype)

One clear option is to have, in addition to the plot icon in the main Acquisition list, an icon for showing the datatype's NWB Widget in a dedicated panel...

Start with the Testing.ipynb example in the NWBShowcase repository and compare its 2D Position/Spatial Series rendering in NWB Widgets with the current NWB Explorer view. Investigate how NWB Explorer identifies and displays datatypes, then define the required interaction and verify that the example renders through the intended NWB Widget support.

Written by the indexing model from the issue text.