Add python shareddatalayer API and public exceptions.

Add python shareddatalayer API and public exceptions.

Added synchronous API functions:
* To read, write and remove from SDL storage.
* To read, write and remove from SDL group.
* To acquire, release and control an SDL lock entry.

Defined a set of SDL exceptions what SDL python implementation
will raise when there happens an error either in SDL or in
the backend database (Redis) what SDL utilizes.

Change-Id: Iaf0f4b3052d2cf189feadf2eb506b7e9a8463409
Signed-off-by: Timo Tietavainen <timo.tietavainen@nokia.com>