Remove SupySandbox

[Mikaela]

This can always be recovered with git. I am removing this, because this causes errors in the Travis CI build and pysandbox's readme has the following notice:

!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
!!! WARNING WARNING WARNING WARNING WARNING WARNING WARNING WARNING !!!
!!!                                                                 !!!
!!! pysandbox is BROKEN BY DESIGN, please move to a new sandboxing  !!!
!!! solution: run python in a sandbox, not the opposite!            !!!
!!!                                                                 !!!
!!! Learn more about pysandbox failure:                             !!!
!!! https://lwn.net/Articles/574215/                                !!!
!!!                                                                 !!!
!!! WARNING WARNING WARNING WARNING WARNING WARNING WARNING WARNING !!!
!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

[Mikaela]

Other options would be:

• disable tests for pysandbox
  • I don't understand .travis.yml enough, because of the if.
• add pysandbox to requirements.txt. It's not in PyPi anymore, so the entry would be git+https://github.com/haypo/pysandbox.git

[progval]

I like option #2. Can you do it?