Private call parking via API

There is a need to park calls privately, which is facilitated today via the Park Location feature in the admin console. However, in order to facilitate workflows managed by external systems via an integration, API functionality is needed. Specifically:

* An API to retrieve a list of Park Locations
* The Park Call API needs to be enhanced to allow a developer to specify a Park Location ID

For completeness, it would also be helpful to enable full create/update/delete operations for Park Locations so that they can be managed remotely as well.