R1:420235f9c4e1

Drag-drop file upload.

Summary:
- have files be uploaded by drag+drop instead of browse.
- Files are named by their uploaded filename, the user isn't given a chance to enter a file name. Is this bad?
- Store author PHID now with files
- Allow an ?author=<username> to limit the /files/ list by author.
- If one file is uploaded, the user is taken to its info page.
- If several are uploaded, they are taken to a list of their files.

Test Plan:
- Quickly tested everything and it still worked, I'd recommend…