R1:b89e6c0fa91a

Add "idea://" to the upstream editor whitelist

Summary: This supports the IntelliJ IDEA editor.

Test Plan:
- Looked at the editor settings panel, saw "idea://".
- Set my editor pattern to "idea://a?b".
- (Did not actually install IntelliJ IDEA.)

Differential Revision: https://secure.phabricator.com/D21206