Put file name in view URI, so downloading it with option-return creates a usefully-named file

Summary:
If you Command-L + Option-Return to download stuff off, e.g., Paste,
you get "PHID-FILE-ad98abg9bsd9ashbs.txt" in your download folder. Put the file
name in the URI instead, so you get a reasonably named file.

Test Plan: Downloaded some files, got reasonable results.

Reviewers: btrahan, jungejason

Reviewed By: btrahan

CC: aran

Differential Revision: https://secure.phabricator.com/D1427