Refactor FOA interface to use HOA implementation

[joslloand]

There are a few reasons to refactor user facing FOA implementations:

1. simplify maintenance
2. reduce footprint
3. clarify implementation of theory

Given that not all FOA operations are analytically possible in HOA, a first step would be to identify which operations (and interfaces) are easily implemented via the HOA codebase.

[joslloand]

See also #60