Castbar: Allow different settings for interruptible and non-interruptible casts

[Backupiseasy]

• https://www.curseforge.com/wow/addons/tidy-plates-threat-plates?comment=5292
  • how can i disable spell icon for non-interruptable spells?
• https://www.curseforge.com/wow/addons/tidy-plates-threat-plates?comment=5290
  • The possibility to change the color of the Interrupt Overlay (General > Castbar > Appearance > Format > Interrupt Overlay).

[Backupiseasy]

Overlaps with: https://github.com/Backupiseasy/ThreatPlates/issues/257