Add deprecation warnings for SdlInstance APIs

Add 'Deprecated:' warning texts to SdlInstance struct type and all
of its receiver API functions. SDL repository contains SyncStorage
struct type with its receiver API functions and it should be used
instead of SdlInstance. With this commit there is added deprecation
warnings and these warnings should be a heads up for SDL API users not
to use anymore  SdlInstance API. After some reasonable time has passed
SdlInstance will be removed completely from the SDL repository.

Issue-Id: RIC-805

Signed-off-by: Timo Tietavainen <timo.tietavainen@nokia.com>
Change-Id: I69d2e9fcfc42111c2e660cc451026c6d713cff70