Merge pull request #1025 from ilastikdev/master

Fixed issue #786
object classification: fix print probabilities bug on right click
serializer: log a message when the input file can't be found.
minor cleanup.
ErrorMessageFilter: Eliminated potential "dictionary changed size during iteration" error.
Never modify the roi parameter provided in propagateDirty().
ObjectClassification: Added JSON label info export/import menu items.
ObjectClassification: Convert labels to 'int' before exporting to json.
ObjectClassification: label export: One more conversion to 'int' for the json export.
OpObjectExtraction: Copy feature dict before modifying it in-place. (Avoid conflicts from other threads.)
BlockwiseObjectClassification: Parallelize prediction.
OpDataExport: Assume that on-disk data is clean upon initialization.
OpBlockwiseObjectClassification: Added metadata for ram usage and blockshape
Adds 2D Convex Hull and 2D Skeleton Features plugins to the Feature Selection Dialog.
Fixes an ordering bug in SubFeatures selection dialog ('advanced' keys values were not set).