SgEngitySchemaInfo now loads unsupported fields from XML caches

Unsupported fields written to a schema cache XML file are now also
loaded when reading a cache XML.
SgFieldEntityMulti.value() returning None fix

SgFieldEntityMulti.value() returns None when it should return an
empty list.  Example: A sequence that contains no shots the "shots"
field should return an empty list not None.
SgProject.shotNames ignore sgSequences arg

SgProject.shotNames now passes sgSequences to SgProject.shots.