Provide 'advance' orange widget designs

See merge request !16

This reverts commit 2c0d2cfa.

- default static_input values are None instead of MISSING_DATA: otherwise cannot process
- avoid call to handleNewSignal as there is no default value
- check the workflow can be executed and is provided the expected result
- update example add-on 2: sumlist_tutorial

This class will create one thread for each task run requested.
No progress is associated as we could have some conflict

Add an example in tomwer-add-on-2: SumListSeveralThread

* in binding: add OWEwoksWidgetOneThread
* in add-on example 2: add OW "PrintSumOW" to complete the example

This classe handle boiler plate code for link between orange3 and ewoks.
This should be the Base class of all Orange widget class that can be translated to ewoks.

Ci orangefork

See merge request !9

Task should be gui free

[registration] try first to load WidgetDiscovery from the old Orange.canvas.registry.discovery, then on orangewidget.workflow.discovery

[registration] try first to load WidgetDiscovery from the old Orange.canvas.registry.discovery, then on orangewidget.workflow.discovery

This reverts commit 91352b2d.