Add Critical CVE Severity to support CVSS v3 scores 9.0-10.0

[xingzhang-suse]

Case: NVSHAS-8242

Add CRITICAL labeling throughout the interface to include CRITICAL in addition to HIGH and MEDIUM. Use CVSS v3 levels to apply correct criticality per CVSS v3 specs. Always use CVSS v3 values by default and move this option to a Settings page for the UI.