Issue 137 - Allow formatter to set url_only and url_plain.

[rosiel]

GitHub Issue: #137

• Other Relevant Links (Google Groups discussion, related pull requests,
  Release pull requests, etc.)

What does this Pull Request do?

Puts the "URL only" and "Show URL as plain text" checkboxes on the field formatter settings page for authority links

What's new?

• The parent, LinkFormatter, "locked down" those fields from inheriting classes by setting their access to true only if you're in a Link Formatter. This PR does the same, setting their access to true if you're in an Authority Link formatter.
• Does this change require documentation to be updated? No
• Does this change add any new dependencies? No
• Does this change require any other modifications to be made to the repository
  (i.e. Regeneration activity, etc.)? No
• Could this change impact execution of existing code? No

How should this be tested?

A description of what steps someone could take to:

• Reproduce instructions are in [BUG] Authority Link field formatter's setting form doesn't allow you to set url_only or url_plain. #137.
• With this PR, the Authority Link formatter should also show "URL only" and, if that's checked, the other checkbox.

Additional Notes:

Any additional information that you think would be helpful when reviewing this
PR.

Interested parties

Tag (@ mention) interested parties or, if unsure, @Islandora/committers