RequestManageCredentials landscape mode

* Split screen into two halves, where the left
  side includes the title and the right side
  includes the recycler view, floating action
  button and action buttons.
* https://screenshot.googleplex.com/6Co6kn2DyXZRGNZ
* https://screenshot.googleplex.com/6uwHAGuRHjNcStN

Bug: 189193577
Test: manual testing via TestDPC
      RequestManageCredentialsTest
Change-Id: I9c82a7471c885658aacb40b22166ec801e2833ca