ENH: Add Markups module providing easy fiducials management.

Based on the Annotations module from Slicer 4.2 and the Fiducials
module from Slicer 3.6, add a new Markups module to provide
some missing functionality into Slicer4:
- one file per fiducial list
- added a unique id and orientation for each fiducial
- save/restore default display settings
- create list with current list display settings
- press p to add a fiducial
- one click jump slices
- move fids between lists
- split displayable managers into 2d and 3d versions

Non module specific changes:
- updated the mouse mode tool bar to be more generic, requiring
some changes to the vtkMRMLSelectionNode:
Rename the selection node annotation variables to place node.
Renamed the active annotation id to active place node class name to
match what it was actually holding.
Use the active place node id for just the markups since the annotation
logic keeps track of the active hierarchy.
Add an icon name string so that the tool bar doesn't have to derive
it from the class name.
- updated the Annotations and TractographyFiducialSeeding modules
- updated the Command Line Module Logic to support LPS:
Add coordinate system flag to the WriteCLI method on
displayable nodes.
- added custom actions to qMRMLNodeComboBox
- add missing load utility methods for annotation and markup fids
Added loadAnnotationFiducial to load a single annotation fiducial from a
.acsv file.
Added loadMarkupsFiducialList to load a list of markup fiducials
from a .fcsv file.