Add data explorer formatting option to truncate large strings or binary values, truncate by default

[wesm]

There is currently no limit on the size of individual values that can be returned in a get_data_values request, which can create serious performance or memory use problems if a dataset has large string or binary data values within columns (which can be arbitrarily large). We should add a formatting option to truncate at some reasonable limit by default, and if we need to display a full value, we have the ability to export it with export_data_selection.

[softwarenerd]

*And binary data.