Scripts for building Orange application installers

To build installers for a specific release, create a new branch under releases e.g.releases/3.8.0, edit the GH Actions config files to replace BUILD_BRANCH with the required branch or tag (i.e. 3.8.0) in the orange3 git repo. Also replace BUILD_LOCAL from 1 to "" if binary packages are already available from conda-forge/PyPi.

Built installers are kept as build artefacts of the workflow runs.