Filter Known Files

Adds options to General Options panel to filter known files in the data result viewers when selecting nodes under "Views" or "Data Sources". By default, it filters under "Views" and not under "Data Sources". 

Implemented by wrapping the DataResultFilterNode in a KnownFileFilterNode (which then gets wrapped in a TableFilterNode) before it is handed to the DataResultViewer. The new filter node doesn't do anything unless the option for the selection context is set. (Which means, for example, if the node is selected from "Views", but the option to filter under "Views" is not set, it won't do anything).