Pull Schema, Topology, and Hierarchy Utilities into Separate Library

[U8NWXD]

Scattered throughout Vivarium, we have functions to perform operations on schemas, topologies, and hierarchies, e.g. inverse_topology. I think the codebase would be easier to understand if we pulled these functions into a new library under vivarium/library so that we can document and test them thoroughly.

In this library, we would have 3 kinds of entities:

• Hierarchies are trees of data.
• Schemas assign metadata to each node in the tree.
• Topologies are like MongoDB projections. They describe how to retrieve data from a hierarchy and re-shape it into a desired structure.

The library would provide functions to do the following:

• Reach into a hierarchy and retrieve values in the form specified by a topology.
• Invert a topology (this function takes in one topology and returns a new topology).
• Given a set of schemas and a set of topologies, create a hierarchy. This function should take parameters to describe how to initialize the hierarchy values from the schema rather than hard-coding a special key like _default. This also shouldn't be dependent on the Store class.
• Take a hierarchy and figure out what schemas need to change to effect a change in that hierarchy. This function will also need to take the schemas as an argument.
• Perform operations (e.g. updates) over a hierarchy based on a set of schemas.

Possibly related: #100