Playgrounds to be moved to separate repository

Action required for those who have playgrounds:

We are moving them out of the matsim git repository into their own one. See e.g. MATSIM-676 - Getting issue details... STATUS  or MATSIM-685 - Getting issue details... STATUS  or MATSIM-680 - Getting issue details... STATUS for discussion.

This mostly means that you will have to check out this new repository separately, and put it next to the current repository into your (e.g.) Eclipse workspace. (Don't try to put it inside the current repository.) IDEs like Eclipse don't care much – they resolve dependencies within the same workspace on their own.

On the other hand, it means that if you are developing neither the core nor a contrib, you now probably need to check out only the playgrounds!

I plan to do this on 2017-06-29. I will briefly block pushes to matsim, create the new playgrounds repository, and re-open matsim. It will be easiest if you have everything committed by that time – though it should also be easy to transfer your changes to the newly checked-out playgrounds repository. After all, the directory structure is not going to change.