Integrating self-registration with carbon `claims` management

A new jaggery module - `claims` is added to interact with Carbon claims management and retrieve claims for given dialects. 

The registration forms are changed to render the `required` claims of the default claim dialect as specified by the `DEFAULT_CLAIM_DIALECT` of `claims` module. 

Upon user self-registration, the rendered user fields mapped to claims are stored via the carbon  `RealmService` alongside the now-existing `username` and `password`.