Refactor configuration management about mlonmcu

[PhilippvK]

Another problem we have in the current implementation is the following:
We can currently not guarantee the types a config option, aka we have to explicitly cast everything using a @property to access the dict. However, special cases such as None should be handled differently which would increase the complexity of such "getter" functions.

In addition I found the issue that we currently can not detect false via the command line option because bool("false") does return true. Instead we would need bool(distutils.util.strtobool(some_string)) which should not be user-facing and indeally happen automatically. An alternative would be a similar approach to the configuration passed via the environments.yml. Here, booleans seem to be detected automatically, but I have to double check that. Eventually using ast.literal_eval(x) would help as well.