lms now depends on the nginx role
Public keys, pingability

* Add developer public keys to the repo, provision logins for them
* Add SecurityGroup stanza to make brought up hosts pingable
Simple JSON linter

* To autocheck on every commit:
  ```cp git-hooks/pre-commit .git/hooks/pre-commit```
Adding pre-commit and post-checkout hooks

* Pre-commit hook lints JSON
* Post-checkout hook causes hooks directory to update with current
  project hooks
* Readme updated so installation section reminds you to install hooks