Fixing bug 481431 for the MOOSE Item and MOOSE Form Editor by adding a
subclass of XMLFormContentDescriber that validates whether a file is
both a MOOSE Workflow XML Form. 

Updated the XMLFormContentDescriber test to be easily extended to new
content describers, also adding a long overdue
org.eclipse.ice.client.widgets.moose.test bundle and a
MooseXMLFormContentDescriberTester. 

Signed-off-by: amccaskey <mccaskeyaj@ornl.gov>