Create new asset from user dashboard

* Implemented creation of buckets and rivers from the
content view in the user dashboard

* Added a template - "create-bucket-modal-template" to be used
when creating buckets. This template is used by CreateBucketModalView
Backbone view

* Bind the click event that triggers the transition to the create river/bucket
view in BaseAssetListView. This ensures that the binding is cascaded to
objects that extend this class