Header thumbs 2.6

Header thumbs v2.6 changes:

Now using abstracted file system.

Header thumbs v2.5 changes.

Clicking header thumb image now links to post.

Header thumbs v2.4 changes:

Added alt attribute to img element.

Header thumbs v2.3 changes:

No longer requires a specific image handler. File system operations now using XenForo file functions.

Header thumbs v2.2 changes:

Added Limit to options page. Header thumb menu now show the last 300 header thumbs recently shown.

Header thumbs v2.1 changes:

Fixed issue dealing with header thumbs sometimes not updating due to cache.

Header thumbs v2.0 changes:

Added Header thumbs menu. This allows viewing the past 30 header thumbs which have been displayed.

Header thumbs v1.9 changes:

Fixed issue with thumbs not having the correct link.

Header thumbs v1.8 changes:

Updated template modification description.

Header thumbs v1.7 changes:

Fixed problem where Include forums in Options was not selecting forums properly.