Added numeration in workflow steps collapsible buttons

Compare View Link: https://github.com/paulcm/LongitudinalPETCT/compare/9b6d4b8fb119fe538a2956288bd2e50ba15dfa5b...master

Follow-up commit after major Longitudinal PET/CT Analysis Extension update which included the following changes:

DICOM Plugin updates:

    DICOMLoadable caching for performance improvement
    Selection from multiple CTs for PET
    PET only support
    Usage of PETSUVImageMaker module to generate normalized volumes

Module updates:

    Registration of PET/CT studies image volumes
    Quantification: use of PETSUVImageMaker for SUV normalized PET image volumes
    Module settings sidebar
    PET color selection presets
    CT Window/Level selection presets
    ReportOverview Table provides statistics in cells
    Additional segmentation statistics: StdDev, Count, Volcc, Volmm3