change to native Dialogs if possible
object feature selection.

* new feature selection dialog.

* features implemented in plugins.

* new dependency, yapsy, for plugin management.
Fix issue #227
clean up carving applet
work on path input of ilastik.py
save selected object features
Changed order in which applets are created and connected in IlastikShell in order to fix Issue #229. It should be fixed now.
remove brush size names, #256.

Still todo: adjust "Size:" string in GUI to read "Brush size:"
use new signature of notify_failed
belonging to commit on Issue #229 and work on the ilastikShell
carving: implement navigation to position of maxmimum uncertainty
OpEnsembleMargin: Copy roi before modifying it.
Merge pull request #263 from bheuer/DisableDownstream_fix

Disable downstream fix
object features may be selected by clicking on text
OperatorSubView: Added current_view_index() convenience function (and test).
use convenience functions for file selection dialogs, use native dialogs by default
Moved OpH5WriterBigDataset to ioOperators.py (fixes #251)
Merge pull request #270 from christophdecker/master

 Moved OpH5WriterBigDataset to ioOperators.py (fixes #251)
replaced __del__ methods in ProjectManager and ProgressDisplayManager as partial fix of #254
update headless shells for #issue254