* De-crappified JS upload dest check feature. Converted to sajax framework. Comprehen...

* De-crappified JS upload dest check feature. Converted to sajax framework. Comprehensive destination checking like the previous behaviour on submission. 500ms typing delay for rate limiting, response cache. Don't display the warning on submission if the user has already seen it via AJAX.
* Added support for static member functions as AJAX callbacks.
* Moved all upload-related javascript to upload.js.
* Needs artwork, see TODO in upload.js.
* Removed UploadForm::showSuccess() as per wikitech-l discussion. Redirect to description page unconditionally.