ENH: implement #2206 and #2983

Since the browser is raised when the module is entered, people
naturally think that pressing the button that enters the module
will also open the browser; but when the module is already active,
selecting the module is a no-op and the browser is closed.

With this change, the action will also raise the browser when
the module is active, so it conforms with expectations.

git-svn-id: http://svn.slicer.org/Slicer4/trunk@21777 3bd1e089-480b-0410-8dfb-8563597acbee
BUG: fix a warning message when dicom file has been deleted

The Recent Activity widget now gracefully handles the case where
files have been deleted that are referenced in the database.

git-svn-id: http://svn.slicer.org/Slicer4/trunk@21778 3bd1e089-480b-0410-8dfb-8563597acbee