Environment rework

[PhilippvK]

First take on #33 after one year. Work in Progress.

Done:

• Update example environment file dev.yml.j2 to use new format
• Add version field to enironment files
• Add classes for loading/exporting new environment file format
• Add converter to automatically convert outdated files

Remaining tasks:

• Auto-detect version / assert correct versions
• Test of the new environment config leads to issues using MLonMCU
• Add unit tests
• Deprecate the old format. At some point delete old code alltogether (we should be able to get red of a few 100 lines of code)

[PhilippvK]

Should be done until November