R1:2a39fd09ebe7

Bring Javelin into Phabricator via git submodule, not copy-and-paste

Summary:
Javelin is currently embedded in Phabricator via copy-and-paste of prebuilt
packages. This is not so great.

Pull it in as a submodule instead and make all the Phabriator resources declare
proper dependency trees. Add Javelin linting.

Test Plan:
I tried to run through pretty much all the JS functionality on the site. This is
still a high-risk change, but I did a pretty thorough test

Differential: inline comments, revealing…