aurum: Use Aurum namespace

aurum: Use Aurum namespace

This is for prepare Aurum 1.0 version release.

namespaces - Aurum for public classes
             AurumInternal for internal headers such as atspi, impl classes
             AurumInternal::Mock for Mock wrapper.

We will add more namespace if we added other back-end instead of ATSPI,
or other Node type needed.

Change-Id: Ia47ff40387d322e3e0932b3b0cda45b0d4a5f19a