Expose some custom labels

[Joxit]

Add new option HISTORY_CUSTOM_LABELS, this will add a list of custom labels separated with coma

Example: HISTORY_CUSTOM_LABELS=my-first-label,my_second_label

FROM joxit/docker-reigstry-ui

LABEL my-first-label="The Value of my-first-label"
LABEL my_second_label="The Value of my_second_label"

The UI will format your label and replace _ and - with spaces.

closes #160