Fix environment-name behaviour (#50, #54) and add Docker support (#46)

[jonashaag]

• Includes Fix running in Docker container #51
• Not working if name is missing from environment.yml and environment-name is unset #50: Support environment.yml with no name
• environment-name now is a mandatory argument #54: Bring back Micromamba install without environment-name
• Refactor tests

[wolfv]

shall we merge? want to squash?

[jonashaag]

Let's squash if you are happy with the changes.