Rationale:
ManagerImpl and others high level layers are polluted by sip/iax
API dependency. This violate various OOP design rules and
forbids easy future additions, code evolution and debugging.
To solve this issue, this patch implements a Factory design
to create generic Account instances without links to low-level
implementation (SIP/IAX).

Refs #52257
Change-Id: I65afdd80794b317e20f0c65f94246453da7d154f