introducing the unified labeling operator
fixed propDirty mechanism
further fixed propDirty, added unit test for it
changed output type to uint32, added checks and unit tests
OpLabelVolume propagates dirtieness to CachedOutput, too
some cleanup in OplabelVolume
fixed background values in OpLabelVolume
using lazyflow's warn_deprecated instead of logging
Merge branch 'master' into pr-CCL-refactoring

Conflicts:
	lazyflow/operators/opVigraLabelVolume.py
Merge pull request #123 from burgerdev/pr-CCL-refactoring

introducing the unified labeling operator