Refactor usage of creation pattern.

[jamienoss]

Resolves #53 Resolves #67

Changes:

• This propagates the constructor pattern added in #37 to all other classes.
  • adds full init sigs to classes rather than just passing and storing a config.
  • unpacks config to actual instance attributes, i.e., internally stuff isn't ref'd by self.config.attr but self.attr.
  • add *args, **kwargs, and call to super().__init__() to allow for inheritance.
• Some extensions to that laid out in #37 have been added.
  • Ease of conversion between BaseConfig, ConfigDescriptor, and BaseInterface.
  • Add some helper functionality for instantiating nested config descriptors (originally proposed in #35)
  • config & descriptor properties

[jamienoss]

@amitschang comment addressed and back to you for review, please.

[jamienoss]

Thanks for all the reviews.

we can loop back to the chemostat later.

For sure, but just a reminder, these properties were added in #65 not this PR.