Throw dismissible admin notice if we find a font awesome collision

[jonathanbardo]

Plugins like WP Tiles uses an older version of Font Awesome in the admin which cause collision with the newer version we are using.

We should check for common patterns in style registration and throw an admin notice if we find a possible collision. The admin notice should be dismissible by an admin.

[fjarrett]

Related support issue: https://wordpress.org/support/topic/half-the-social-icons-are-missing/

[fjarrett]

@jonathanbardo Perhaps a better way to "detect" Font Awesome would be to scan the global $wp_scripts['registered'] array for paths to font-awesome*.css? It seems more likely that plugins will not register a consistent script handle, and less likely that they would change the stylesheet file name.