Add `make server-offline ...` to makefile so you can run perseus without an internet connection
Add `make server-offline ...` to makefile so you can run perseus without an internet connection

Test Plan:
Disconnect from the internet
Run `make server-offline PORT=9000`
Visit http://localhost:9000 and be amazed

Reviewers: aria

Reviewed By: aria

Differential Revision: http://phabricator.khanacademy.org/D12737

daukantas/perseus,chirilo/perseus,alexristich/perseus,sachgits/perseus,abe4mvp/perseus,ariabuckles/perseus,abe4mvp/perseus,iamchenxin/perseus,learningequality/perseus,ariabuckles/perseus,sachgits/perseus,learningequality/perseus,ariabuckles/perseus,daukantas/perseus,ariabuckles/perseus,chirilo/perseus,alexristich/perseus,iamchenxin/perseus