GUI-1209: Create bucket/folder

Implements the following for https://eucalyptus.atlassian.net/browse/GUI-1209 …

* Create Bucket (linked to from button on buckets landing page and on the dashboard)
* Create Folder (modal dialog opened via button on bucket contents page)
I keep thinking about all of the similar code for handling button enablement, and this. I know this isn't a landing page, but I wonder if we could have a validation controller that could be included? Probably out of scope for here, but something I've been thinking about as our page controllers get bloated with the same kinds of things.