Adding disclaimer and correcting version number

This changeset corrects two things:
1) Corrects the API version number to 2.3.1 as this was the SOL003 document version used.
2) Adds a disclaimer into the description about the draftness of the API definition.

Change-Id: Ic46cdc1f555b830553a5b5dbfa1510a0ac010722
Signed-off-by: Gergely Csatari <gergely.csatari@nokia.com>