Release check and unit tests

To define a methodology for checks to be applied before agreeing each release.

Increase the number of automatic tests within the code to prevent that any new changes to the code affect other parts of the code resulting in bugs that are discovered only after a release.

This will increase the robustness of the tool and the confidence of the users in new versions.

This relates to ID 1 in Roadmap for SEAMCAT development in 2020 which is identified as priority task by WGSE. Task is moved from Jira.