set feature matrix in a different thread to fix #394
When checking for drange, check for non-None instead of 'drange' in meta
shell, workflow: Command-line args that ilastik.py doesn't recognized are passed to the workflow constructor.
Removed obsolete *MainGui.py launch files.  Use ilastik.py for all workflow guis.
shell: Removed unecessary 'SideSplitterPolicy' code, which wasn't being used, wasn't tested, and added needless complication to the layout.