* remove preprocessor flags from public headers.
* split dring.h by manager types to let user include what he needs.
* simplify function relations.
* use namespace DRing for all exported API.
* implement a generic way to export daemon signal callbacks.
* C++11 and project CodingRules conformance.

Refs #65931

Change-Id: I1f1157f9d29e1798ddb27d46e8136bdcb01828dd