This simplifies the finesse.__init__ module by moving configuration loading to a
dedicated submodule. This submodule now has a FinesseConfig singleton that will
generate the barebone user config if it doesn't exist and load it along with the
built-in config on init. This can be loaded directly from modules elsewhere in
Finesse without needing to import _CONFIG from __init__.

Some environment-based functions are also moved to a new module,
finesse.environment.