Examples for testing improved support of NWB Widgets in NWBE

[pgleeson]

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...