ENH: Create new view to embed DICOM browser in main widget
Accomplished through the use of the new view factory qSlicerSingletonViewFactory. Both C++ and Python classes can register any singleton QWidget by calling factory->setWidget(QWidget*) and factory->setTagName(std::string).
The DICOM browser layout is registered as a single view which spans the whole widget. Navigating to the DICOM browser module will change to this new layout and hide the data probe, while navigating to a different widget, loading a series (with browser persistence off), or clicking the new "Close" button, will restore the previous layout and settings.
See discussion: https://discourse.slicer.org/t/dicom-browser-is-stuck-behind-main-window-after-dicom-import/4826/24
