Add status dot key to facets

The “Eligibility status” facet now shows a key of colors to show what each status dot means.
Merge remote-tracking branch 'origin/master' into 1863-status-color-key
Merge remote-tracking branch 'origin/master' into 1863-status-color-key
Merge remote-tracking branch 'origin/master' into 1863-status-color-key
Merge remote-tracking branch 'origin/master' into 1863-status-color-key
Merge pull request #471 from ENCODE-DCC/1863-status-color-key

1863 Antibody status color key in search facet