Refactor BasicImageProcessing plugin to use the new node selection widgets
Summary:
Clean class, remove unnecessary comments, use auto
Remove dead functions
Add single node selection widgets
Use new Qt5 signal-slot syntax
Test Plan: manual UI testing
Reviewers: kislinsk
Reviewed By: kislinsk
Subscribers: nolden, kalali, kislinsk
Maniphest Tasks: T27659
Differential Revision: https://phabricator.mitk.org/D381