Ensure rule/check options can be configured to override default selectors

[marcysutton]

We've made a change to axe.commons.aria.lookupTable to make the API appear less private, as compared to axe.commons.aria._lut. However, rather than creating additional APIs for configuring rules, we should better utilize a tool we already have: specifying options.

axe-core definitely allows you to specify options in checks. Options are also used in the color contrast rule, but we should do some investigating to see if this is actually working. This issue will be satisfied when options can be used to add additional attributes/selectors for existing rules.

The lookupTable could still be used to retrieve defaults, if needed, but in terms of configuring rules, options are the way to go. We should make sure this is easy to do for existing rules with axe.configure, not just custom ones.

[marcysutton]

Closed with #673.

[marcysutton]

An implementation note: this fix does not extend to all rules/checks, but the ones specifically requested (aria-allowed-attr, aria-required-attr). A broader, long-term solution would be to implement an Accessibility Supported API, but that's a huge undertaking and isn't currently prioritized.