Refactoring: Services in MojDbLunaServiceApp

:Release Notes:
Refactor DbService class to MojDbLunaServiceDb and split source files.

:Detailed Notes:
- Move from MojDbLunaServiceApp class that service luna requests.
- Rename class DbService to MojDbLunaServiceDb
- Move class MojDbLunaServiceDb to separated MojDbLunaServiceDb.h and
   MojDbLunaServiceDb.cpp

:Testing Performed:

:QA Notes:

:Issues Addressed:

Open-webOS-DCO-1.0-Signed-off-by: Maksym Sditanov <maxim.sditanov@lge.com>

Change-Id: Ib0fa5089d3ce10903ff7c7cf7bfdab3a2b07ca4a
Reviewed-on: https://g2g.palm.com/3115
Reviewed-by: Build Verification
Reviewed-by: Roger Stringer <roger.stringer@lge.com>
Tested-by: Roger Stringer <roger.stringer@lge.com>