Added jQuery script to check for alerts.

- Added "id" to alert menu item so that the script can change the image src.
- Added script 'alerts.js' this will set a 20 second timeout to check for an alert. If an alert is found will change the alert icon and not check again. If it doesn't find one it will set another timeout for 20 secons.
- Added alert too base.html. (I know this mean the alerts script will be called on auth views but for the time being just wanted to add all js files to site in the same place. A failed call to the endpoint (will return a 403) will mean the timeout isn't reset.
Made i-has-alerts not redirect to signin.

My last commit said that if the user was not logged in the endpoint would only be tried once. This was a __LIE__, I forgot that a 302 was returned when login_required() is used. I now manually check for a current_user object and failing that return a forbidden.