New endpoint to destroy user sessions
Extract verification of authentication to BaseController
Expose authorized spec tag to ensure an endpoint is checking for auth
Check for authorization directly in BaseController
Merge pull request #10 from neighborly/im-destroy-session-endpoint

Sessions#destroy
Add stubs required by the main application
Fix edge case when user sends a request with empty email and password
Add empty json response when requests are 401 and 400 on sessions endpoint

This is necessary because some JS framework don't work well when the response
is empty.