Small updates to API
Small updates to API

Copy/assignment are disabled, new enum values, new
function to get string version of DataType enum, and
clarifications.

Signed-off-by: Patrick Avery <743342299f279e7a8c3ff5eb40671fce3e95f13a@kitware.com>

OpenChemistry/tomviz,OpenChemistry/tomviz,OpenChemistry/tomviz,OpenChemistry/tomviz