Release Notes Datahub 0.3 published on the Datahub pages

News body: 

Published document includes the release notes for the Fingrid Datahub version 0.3 (Stage 3). The document describes the implemented functionalities, existing / resolved deviations and defects in the release. Release includes a B2B message interface using SOAP and a web browser GUI portal.

Link to the Release Notes 0.3