Improves accessibility of private icon indicators

[kimisgold]

This addresses #2334, improving screen reader readouts for public and private indicators throughout the admin interface.

• Public and private toggles have been converted from anchors into buttons.
• Icons that appear in resource lists to indicate a resource's private status have received img roles and appropriate aria-labels. Please take note that this is partially accomplished by adding private status rendering to the linkPretty() function.