proof solver

[hsharriman]

create an MVP proof solver that can finish a proof given partial (correct) state of a proof.
probably use DFS

[hsharriman]

in the checker folder, we want to create a solver, which (for an MVP) takes a CORRECT intermediate proof state (validated by the checker), and then searches for the most optimal path to complete the proof. for the MVP, we can use breadth first search to look for solution paths. Only try to apply steps that would pass (i.e. all its dependsOn would be fulfilled by preexisting steps or it requires no dependencies). for statements and reasons that have multiple arguments, only try one combination of any given set of objects. use the objects stored in ctx to help iterate, rather than using any sort of string permutations to test different arguments for statements.