child user: Add parent_access namespace and rename objects inside it.

Prefixing class names with ParentAccessCode led to too much verbosity
in the code and file names. Addning new namspace fixes that.
Name changes made:
ParentAccessCode -> parent_access::AccessCode
ParentAccessCodeConfig -> parent_access::AccessCodeConfig
ParentAccessCodeAuthenticator -> parent_access::Authenticator

Change-Id: I186e2c12c5b555845c97b27838cbd17da62c6f1c
Reviewed-on: https://chromium-review.googlesource.com/c/1461347
Commit-Queue: Aga Wronska <agawronska@chromium.org>
Reviewed-by: Michael Giuffrida <michaelpg@chromium.org>
Cr-Commit-Position: refs/heads/master@{#631015}
5 files changed