Bulk Theme Publish

Patch adds a new link that lists all populated themes and allows you to select any to bulkpublish. This tool was intended for system administrators and as such the detailed output from any validation failures (ie error, file & line number details) is deferred to the console - the UI just reports overall success or failure. All themes are validated - if any themes are invalid, then no themes are published.

This patch is useful if your site has loads of subsites and all their themes are changed at once. I have not made the visibility of the new link configurable as I felt that it sits quite inoffensively on the screen even if you choose never to use it.

Note the publishing happens in serial and so can take a while - as there is no limit on the number of themes in a site, parallel publishing would carry the risk of running out of memory and there would be the hassle of preventing output from getting interleaved and hence incomprehensible.