ENH: Support for hiding most of DICOM Browser controls through settings

This commit makes it possible to selectively hide most of the controls
associated with the DICOM browser. To hide all controls expect the "Import"
and "Load" button, the following entries should be added under
the "[DICOM]" group in the Slicer settings:

ActionRepair.visible=false
ActionExport.visible=false
ActionQuery.visible=false
ActionSend.visible=false
ActionRemove.visible=false
ActionViewMetadata.visible=false
AdvancedViewCheckBox.visible=false
HorizontalViewCheckBox.visible=false
BrowserPersistentCheckBox.visible=false
DatabaseButton.visible=false
TableDensityComboBox.visible=false

git-svn-id: http://svn.slicer.org/Slicer4/trunk@24117 3bd1e089-480b-0410-8dfb-8563597acbee