Switch to Eclipse RCP 4.11 (2019-03) for JMC 7 GA.

[Marcus Hirt]

Hi all,

The release of JMC 7 has been delayed enough that third party
approvals are starting to become an issue (i.e. they are too old). I
therefore propose the following two things:

1. We upgrade the third party dependencies accordingly for the jmc7 repo.
2. To ensure that this does not happen again, there is now a hard
limit on when the source release of JMC 7.0.0 will happen. After the
upcoming three-week iteration I will declare JMC 7 done. I expect
companies preparing to release binary builds of JMC 7 will test the
last few checkins for the jmc7 repo during this time thoroughly, as
they come in.

Kind regards,
Marcus