BUG: #2326 make save dialog name match node name

With this change, the file save name will be made to match the
name of the node.  This way when a user has specified a
meaningful name in the GUI it will be transferred to the
filename as well for consistency.

http://www.na-mic.org/Bug/view.php?id=2326#c8637

git-svn-id: http://svn.slicer.org/Slicer4/trunk@22004 3bd1e089-480b-0410-8dfb-8563597acbee
BUG: Calculate ruler distance so it's up to date

When adding a ruler node programatically to the scene, with initialised
end point coordinates, the distance wasn't getting updated. Removed the 
local variable that saved the distance and changed GetDistanceMeasurement
to calculate it when called. Still writes out the distance to MRML
but does not read it back in as it will be re-calculated.

Issue #3123



git-svn-id: http://svn.slicer.org/Slicer4/trunk@22005 3bd1e089-480b-0410-8dfb-8563597acbee
BUG: 2528. Fixed the cause of the crash because of invalid LUT in vtkMRMLDiffusionTensorDisplayPropertiesNode

git-svn-id: http://svn.slicer.org/Slicer4/trunk@22006 3bd1e089-480b-0410-8dfb-8563597acbee
ENH: Harmonize qMRMLNodeComboBox properties

Previously, the property currentNodeId of the node combobox was set with an
id (QString) and sent a signal with a node (vtkMRMLNode*) which can be
confusing in the widgets using it. Now, the node combobox as an id
property or a node property.

See Issue #1694
ENH: Add Units module

The unit module handle the unit in slicer. The units are singleton in the
scene that belong to a quantity. So far the only quantity available are
length and time. The units are settings saved with the application.

See Issue #1694
ENH: Add Unit compatible widget

Added new widgets that can observes the MRML scene to deduce the
current unit for a quantity type (the singleton vtkMRMLSelectionNode is
used for storage in this case).

See Issue #1694
ENH: Apply units widget to slicer

Modified:
- Volume info widget: Made it a qMRMLWidget so it can propagate the
mrml scene.
- Annotations: Add to vtk widget and GUI
- Tractography Interactive seeding: Add units to GUI
- Slice controller: add units in spinboxes
- Volumes: add units to GUI
- Editore: add units to paint and island effects

See Issue #1694