Schedule for 1.16.0 release

[Francesco Casella]

After today's discussion at the devmeeting, we agreed on this schedule:

• Release 1.15.0 is cancelled, replaceable support will be available in 1.16.0
• June 1 2020 after the devmeeting: feature freeze on master
• New experimental features which have not been tested thoroughly are allowed until this deadline, as long as they are disabled by default. They can be fixed and improved during the beta testing period, but they cannot be added after feature freeze
• June 8 2020 branch off 1.16.0-beta.1 on the maintenance branch, unless there are major issues. The branched-off version should include replaceable support.
• After 1.16.0-beta.1 is branched off, new features can be pushed on master (1.17.0-dev). Only bugfixes are allowed on the 1.16.0 maintenance branch, of course they should also be applied to the master branch
• Release of 1.16.0 by end of July 2020 at the latest.

There are many open blocker tickets for 1.15.0 and 1.16.0. Since we are switching to time-based release, strictly speaking there is no such thing as a blocker ticket, this is just to give top priority and attention to the fix.

Some of these tickets are expected to be fixed in 1.16.0, the other ones will be rescheduled to 1.17.0