Add credential management app preference to Settings

Background
* This is part of the work to support
  a credential management app on
  unmanaged devices.
Changes
* Add a preference controller which will only
  be enabled if there is a credential management app.
* Add a fragment to display details on the credential
  management app and its policy. Add a remove button
  to remove the credential management app.
* Link CredentialManagementAppAdapter to new fragment
  and add expander.

Manual Testing
* Verify preference is disabled if there is no credential
  management app.
* Verify preference summary shows credential mangement
  app name if a credential management app exists.
* Verify fragment details page displays the
  authentication policy correctly.

Bug: 165641221
Test: Manual testing
      make RunSettingsRoboTests -j ROBOTEST_FILTER=com.android.settings.security.CredentialManagementAppFragmentTest
      make RunSettingsRoboTests -j ROBOTEST_FILTER=com.android.settings.security.CredentialManagementAppControllerTest
Change-Id: I06d6b88d0c89022f7a6cbf3031834defcb54bd51