Backport S-Rep support updates

[jcfr]

This PR back-ports a suite of patches from the SlicerSALT fork to ShapePopulationViewer:

• Full S-Rep support (XML and JSON)
• Robust spoke and fiducial rendering
• A custom colormap loader and CLI flags
• Interactive time-series playback with slider & VCR controls
• Numerous UI/UX refinements
• Critical bug fixes (filename display, camera reset, series validation)

Pending

• Add dependencies to https://github.com/KitwareMedical/SlicerSkeletalRepresentation

Highlights

1. S-Rep Import & Parsing

• XML: Parse <upSpoke>, <downSpoke>, <crestSpoke> elements, append into a single vtkPolyData.
• JSON: Load .srep.json via MRML’s vtkMRMLSRepStorageNode and export using vtkSRepExportPolyDataProperties.
• CLI: Introduce --srepfiles (-s) flag in the standalone viewer; validate extensions before loading.
• CSV Loader: Recognize .xml & .srep.json alongside .vtk/.vtp.

2. Spokes & Fiducials Visualization

• Spoke Geometry: ExtractSpokes() and AttachCellType() produce line meshes with per-point cell-type arrays; automatically compute magnitude scalars for 3-component attributes.
• Fiducials: Read .fcsv markups, compute point spacing to size spheres, tag each with a “Fiducial Index” scalar for coloring.
• Filename Fix: Correct m_FileDir/m_FileName assignment so the Qt UI shows the right fiducial filename.

3. Custom Colormap & CLI Enhancements

• Color Map: Bundle sRepColorMap.spvcm resource; auto-load into the gradient widget on S-Rep import.
• CLI Flags: Wire up --srepfiles and --fiducialfiles options in ShapePopulationViewer.cxx; enforce file-type checks.

4. UI & Layout Refinements

• Import Panel: Switch from QHBoxLayout to QVBoxLayout, then to a grid, reorganizing “Add Directory”, “Add VTK/VTP”, “Add S-Rep”, “Add Fiducial” and CSV buttons for clearer grouping.
• Module Widget: Replace ad-hoc tool-button insertion with named QToolButton widgets (toolButton_Open_*, toolButton_Delete_*), simplifying layout and theming.

5. Time-Series Loading & Playback

• Dialog: timeSeriesLoaderQT displays CSV tables via vtkDelimitedTextReader → vtkQtTableView, emits selected file sequences.
• Initial Frame: Show only the first mesh; slider / spin-box disabled until load completes.
• Slider / Spin-Box: Step through frames, enforcing identical sequence lengths; retain attribute & colormap settings on change.
• VCR Controls: “First”, “Back”, “Play”, “Forward”, “Last” buttons (with embedded SVG icons) and a QTimer for ~200 ms autoplay loops.
• Camera & Alignment: Automatically reset view each step, preserve user-chosen alignment; re-apply camera on every frame.

6. Bug Fixes

• Fiducial filename now displays correctly in UI.
• Slider is disabled/enabled appropriately, resets to zero on new loads.
• Camera is reset on each time-step change (pushButton_VIEW_reset).
• CSV loader messages updated to include all supported extensions.

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This consolidation brings ShapePopulationViewer on par with the SlicerSALT fork’s advanced S-Rep and time-series capabilities—ready for integration into our mainline.