Make aborted and disabled icon colours themable

[Jonny-vb]

Update the aborted and disabled icon colours to be set from variables instead of hard coded colours, allowing them to be overwritten by themes.

See:
jenkinsci/dark-theme-plugin#550
jenkinsci/dark-theme-plugin#552

Testing done

No tests written as is a pure UI update

Proposed changelog entries

• Make pipeline icons for aborted and disabled themeable

Proposed upgrade guidelines

N/A

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Desired reviewers

@timja

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[janfaracik]

LGTM - need to confirm this is needed though jenkinsci/dark-theme-plugin#550 (comment)

[timja]

I would like to understand this before we proceed:
jenkinsci/dark-theme-plugin#550 (comment)

but once thats understood this is good

[timja]

@janfaracik has figured it out in jenkinsci/dark-theme-plugin#550 (comment)

This needs fixing in branch-api-plugin

[timja]

Alternatively adapting ballColorTd may be enough:
https://github.com/jenkinsci/jenkins/blob/master/core/src/main/resources/lib/hudson/ballColorTd.jelly