add a licence (was ACTS-84)

Original author Christian Gumpert @cgumpert

Add a license file to the GitLab repository. The tentative conclusion of todays meeting was to go for LGPLv3 if no other constraints arise. The question, where this license needs to be referenced, is still open.

Edited Mar 27, 2019 by Moritz Kiehn

To upload designs, you'll need to enable LFS and have an admin enable hashed storage. More information