Patch Release 3.1.1

We are happy to announce the first patch release in the 3.1 series of Allpix Squared, version 3.1.1.
This release contains 43 commits over the feature release 3.1.0 and fixes a host of issues discovered by users across the framework.
The release is available as Docker image, CVMFS installation and source code from the repository.

The following changes have been made: