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)
@dkavanagh : I'm going to refactor (and fix) the checkbox fields across the app in GUI-1234, so feel free to merge this PR if your code review is complete.