[PF6] Change Battery to Severity

[fhlavac]

Update the Battery component name to severity and update its implementation to use new PF6 severity icons UXD issue here

[kaylachumley]

I second this update! Would be good to have this update reflected on org. @fhlavac

[fhlavac]

@kaylachumley definitely, we plan to incorporate this change into some of the first releases of component-groups based on PF6

[fhlavac]

closing in favor of #222