Fixes #5409: Adds visible :focus styles for nearly every link/input

* For many links/icons, duplicates hover style on focus
* For tabs/owner/page links, adds underlines on focus
* For images, lowers opacity on focus
* Allows browser default focus style on inputs like checkboxes & selects
* Normalizes text/input focus styles on url/email/password inputs
* Adds dotted outlines on just a couple links

Basically you can visibly tab through almost every link on most pages. This is motivated by my own frustration using forms on elgg, not being able to see focused links/button.