Added Tables support
- New module added: Tables. Create create/view/edit/delete tables, freeze column/row header, lock to read-only (vtkMRMLTableNode).
- Tables can be shown in the view layout (new layout added: Four-up table, more can be added as needed)
- Load/save csv, tsv, txt files as table nodes
- Copy-paste to/from Excel
- SubjectHierarchy plugin (show/hide, edit, clone tables)
- Use tables as input/output for CLI modules (PET Standard Uptake Value Computation module is updated to use tables; there was no need to change the Slicer Execution Model, the Table data type was already usable)
- Reusable widget added for viewing/editing tables in C++ and Python modules
Demo video: https://youtu.be/tNrAut6WD_k
This pull request is to facilitate testing and review, I'll squash all the commits and integrate when the trunk is not frozen anymore and other pull requests are merged.