Merge pull request #30 from edx/features/jbau/npm

npm install  playbook

playbooks/roles/npm/tasks/main.yml

+# requires:
+#   - common/tasks/main.yml
+#   - ruby/tasks/main.yml
+---
+- name: Install nodejs, and by extension npm
+  sudo: True
+  apt: pkg=nodejs state=present install_recommends=no
+  tags:
+  - npm
+  
+- name: Install mitx npm dependencies
+  shell: npm install chdir=${app_base_dir}/mitx
+  tags:
+  - npm
+