/images/icons/favicon.png is not up to date

The JIRA remote issue link code assumes that the favicon PNG is located at /images/icons/favicon.png. This icon hasn't been updated in 4.1, however, so JIRA is displaying the old-style icon.

We need to support linking to multiple versions of Confluence, so we can't use any of the new images in /images/logo.

Although Confluence doesn't use this file anymore, it is referenced in CONF-8247 (Favicon customization) so it is one of the de facto locations of the Confluence icon