list directives in a list instead of a long string

Same intent as in https://github.com/rwjblue/ember-cli-content-security-policy/pull/15, but coming from a branch and with a couple of tweaks.

Instead of:

'script-src': "'self' https://cdn.mxpnl.com https://cdn.foobar.com"

Do:

    'script-src': ["'self'",
                   "https://cdn.mxpnl.com",
                   "https://cdn.foobar.com"]

Handles:

    contentSecurityPolicy: {
        'style-src': ["'self'", "'unsafe-inline'"],
        'frame-src': "'self' http://disqus.com"                                    
    }

And prints a deprecation warning to the server.