Fix OTBApplicationOutputImageChanged and ExecutionDone slots not being called

Summary

Fix a bug where output images are not loaded after app execution in monteverdi.

It was introduced by the combination of !161 (merged) and !441 (merged), it was caused by two problems:

• Overriding a non virtual slot in mvdQtWidgetView.h
• Broken signal/slot connection using the old Qt syntax in mvdMainWindow.cxx

Fixed by making the overriden function virtual, and using the new Qt 5 syntax for signal/slot connection.

Rationale

Fix the bug.

Copyright

The copyright owner is CNES and has signed the ORFEO ToolBox Contributor License Agreement.

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Check before merging:

• All discussions are resolved
• At least 2 votes from core developers, no vote.
• The feature branch is (reasonably) up-to-date with the base branch
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• Copyright owner has signed the ORFEO ToolBox Contributor License Agreement