* Wrapped zipping of layout images in try/catch block to prevent exceptions when there is no thumbnail image
* Introduced a more elegant way to include necessary script files (jQuery et al.) in Site.main_js_action()
* Slightly modified jQuery "onload" calls
* Removed obsolete skin files (ie. content moved to the protected skin file)
* Moved contents of Messages.skins to their protected siblings
* Prefixed notification skins (used in e-mails) with "notify_"
* Fixed and simplified a whole bunch of issues in compatibility layer
