Feature/video codec phonebook clear

[TrevorPayne]

Modified the SelectDirectoryEntry method in VideoCodecBase to accept a 0 index and set the private _selectedDirectoryItem to a null value, and modifed the rest of the method to clear all appropriate trilist signals.

Added a digital join to explicitly pass a zero index to SelectDirectoryEntry and set the DirectorySetRow join to a ToFromSimpl so we could report the index passed into the method.