feat(rxStatus): attr edit for success/error banners; Resolves #420

Addresses issue #420, adding timeout and repeat=false attributes to success banners and a repeat=false attribute to error attributes. Once this is merged in, I will need to delete `status.js` and `status.spec.js` from encore-cloud-ui and remove the import of `status.js` from encore-cloud-ui's `index.html`.
I'll do so. So everyone knows on github: much of this conversation started on an internal JIRA ticket (https://jira.rax.io/browse/EN-760) which came out with the following conclusions: that repeated success and error messages should be combined, and that success banners should time out (`dismissible` will still be set to true.) - gives folks a heads-up, saves users from a click.