Add internal plumbing to DPM for encryption

* Add code to persist per-admin setting
* Add hooks for OS-level tie-in (is supported, get / set status)
* Add 3rd API call to get OS status (irrespective of admin settings)
* Remove "REQUESTED" status, no longer relevant with 3rd API
* Fixed bug that impacted global proxy settings
* Update api/11.xml to match current.xml

Bug: 3346770
Change-Id: I56bdf9a7894f6ca4842402c7b82ddb3caf4b37b9