Remaining things to complete:
* In WebKit, the button images are offset +5 pixels down. They shouldn't be.
* Small "+" buttons under notebooks and the note tree are broken.
* Toolbar resizing doesn't work anymore (TODO comment).
* new toolbar button for attaching a file
* button opens new Upload_pulldown() for uploading a file
* began controller.Notebooks.upload_file() to process the upload
browser-specific CSS hack and looked crappy. Those elements that are still
rounded are now implemented with nice smooth images instead.
Also changed downloaded HTML generation to specify sans-serif for the font.
Dan Helfman