Release notes and dependencies for v15r2 release

This is a release on master necessary to release DaVinci and Panoramix. It has very few changes with respect to the previous v15r1.

mentioned in merge request DaVinci!375 (merged)

@nskidmor @atully @cvazquez could you please check, merge and make a tag? We should make a Panoramix (and a DaVinci release) before we merge incompatible changes there.

merged

mentioned in commit a80b2c05

@rmatev Done

thanks!