slot: If an exception is caught during disconnect() while we're already handling an exception, print the second exception but continue raising the first one.
Operator: Added support for the special NOTREADY metadict attribute, which can be used by an operator during setupOutputs to specify that a specific slot is not actually ready, despite the fact that setupOutputs completed without any errors.
OpSingleChannelSelector: In setupOutputs, Output.meta.NOTREADY if there aren't enough input channels to provide output yet.
schematic: Color-code slots according to their ready status
OpVigraWatershedViewer: Added a fixme.
Op5ifyer: Copy all metadata from the input.  Also, add 'original_axistags' and 'original_shape' metadata attributes.
IO Operators: Don't accept a default axis order (users must use an Op5ifyer), and don't automatically insert a channel axis to the output shape.
Copied testOp5ifyer from volumina repo.
OpNpyFileReader: Removed a (now) incorrect assertion.
Fixed io operator tests.
OpInterpMissingData: Bug fix: Removed a shortcut path in execute() that wasn't correct.