New File and Image functions: Revisions and more

The CMS functions for uploading images and files have been reworked. A major new feature is the ability to upload a new version of an existing file or image. The new version will automatically replace the old one across the site. Previous revisions can be saved for posterity. It's also now possible to edit details of existing files and images (like the alt text for an image), so one doesn't have to delete and replace as with the old tools. All these functions are also now available in project-specific document archives.