Adds support for jade helper functions.

Just add a helper function to `views/util.coffee`, and call them as
'util.<name>(...)` from a jade template.
Re-enabled chosen initialization on form selects.
Setup attributes for related (linked) resources on models.

The `relatedLinks` property on a model specifies a mapping of
link relation to model object that is used to create model
instances.
Also create a base URL for API requests on the base entity.