News updates for 2.7.0 beta2

Mention most relevant updates and user visible changes and fixes.

These entries will only be maintained during the beta/rc series, but
will then be replaced with a single "2.7.0" entry when we will release
2.7.

Signed-off-by: Guido Trotter <ultrotter@google.com>
Reviewed-by: Helga Velroyen <helgav@google.com>