Add .arcconfig

Summary: Need a .arcconfig to use this repo with phabricator.

Test Plan: Run arc diff.

Reviewers: arigrant

Differential Revision: http://phabricator.afterburner.me/D1
Add git push on diff

Summary: Travis-CI needs code to be in git before it can build it. This adds a post-step to arc diff to push the code toa scratch branch.

Test Plan: arc diff

Reviewers: arigrant

Differential Revision: http://phabricator.afterburner.me/D2
Add vim .swp files to .gitignore
Have Travis-CI watch ci/... branches