allow configuration of views

Currently views can only be created / deleted but not configured (beyond the view type).

This PR adds a `update_config()` method to the `view` class which is symmetric to the same function in the `job` class (https://github.com/salimfadhley/jenkinsapi/blob/d0ed211b8415ccf38628c81b3ca0a429bc7da90d/jenkinsapi/job.py#L522).