Added node title background highlights for selected nodes.

(transplanted from orange/572797f576ade81d53a9da0f1bf8fa2c3818ba0d)
Do not truncate an existing file in case of an error in 'save_scheme'.

(transplanted from orange/bdf2527fe91799412a2fa73038e1a6a3a5f783ce)
Fixed an UnboundLocalError in IntesphinxHelpProvider.

(transplanted from orange/53ad9ec6931d495d896f066d0895908e2d030e1c)
Disconnect the SchemeNode from the widget when it has been removed.

(transplanted from orange/dbcc370d05059e2a52d8e3d9291f8fa5031d10c9)
Initialize the SchemeNode state messages on widget initialization.

(transplanted from orange/41d75ac844c92a6df3f9dd311842e386bc3aa1c8)
Delete a reference to a widget when it is deleted.

(transplanted from orange/4d06c658ad17c239a4a86c8cb11ad079501746df)
Fixed NodeItem progress state initialization and updating.

Progress indicator should only be visible when the node is
in a "processing state".

(transplanted from orange/975cc3daadf35924ee5b9ca3af21c4698cdf6b4d)
Fixed an AttributeError in DragStartEventListener.

The 'buttonDownObj' member variable can already be None if another
drag/drop operation starts and completes  within the
'dragStartOperationRequested' signal propagation.

Use the local stack variable to access the button instead.

(transplanted from orange/872337b35d3c9c80650eacc5b2a6147446d17b01)
Ensure the NodeItem shows a visual progress indicator even at 0% progress.

(transplanted from orange/5fd8d0445790928782dda1cfc1a6d3185cc55495)
Make sure the opened widget window is active and has keyboard focus.

(transplanted from orange/13b11307771636e7296c59340243fcf42f27e52d)
Added progress bar state tracking in OWWidget.
Initialize the tracked processing state property.

(transplanted from orange/41a3f530528cee708beaca380dcb26fbf2fb9851)
Fixed widget progress bar initialization.

(transplanted from orange/a34f5c6868697439da3d9b615e56262d9690f2ae)