Fixes http://www.na-mic.org/Bug/view.php?id=2109

Now any module can associate a MRML node type with a module (instead of having a hardcoded list of modules
in qSlicerApplication) and when switching to a module, the chosen node is selected as active node.
Associations can be added by calling qSlicerApplication::registerNodeModule().
Multiple modules can be associated with the same MRML node type.

The best module for a specific node instance is determined run-time, by calling
qSlicerAbstractModuleWidget::nodeEditable() for each candidate and choosing
the one that has the highest confidence in handling the node.
This mechanism is used for selecting the CLI module that corresponds to a specific CLI module parameter node.
This mechanism is also used for switching to volume rendering module if a volume rendering clipping ROI node
is selected for editing (instead of switching to the Annotations module).
The most suitable module's qSlicerAbstractModuleWidget::setEditedNode() method is called to select the currently edited node.
qSlicerAbstractModuleWidget::nodeEditable() and qSlicerAbstractModuleWidget::setEditedNode() methods can be overridden
in scripted loadable modules as well.

As edited node selection is now possible using a clean, unified method call, it is no longer necessary
to access GUI widgets directly. Therefore, almost all editProperties() method calls in subject hierarchy plugins were
removed (replaced by a common implementation in the base class). This new, simplified method fixes robustness issues
of using node name filters for selecting a node in model hierarchy, inability to choose annotation hierarchy nodes, etc.

qSlicerAbstractModuleWidget::setEditedNode(vtkMRMLNode* node, QString role, QString context) has two extra (optional)
arguments. Role can be used to specify additional nodes for a module (e.g., if there are multiple inputs for a module
then role argument can select between them). Context can be used for specifying a sub-selection within a node (for
example, Segment Editor module can be activated for a selected segment - specified by 'context' - of a specific
segmentation node - specified by 'node').

Fixed code review errors (typos and API simplification).

git-svn-id: http://svn.slicer.org/Slicer4/trunk@25003 3bd1e089-480b-0410-8dfb-8563597acbee