Update SAT object

  - Rename getFromFile() to initFromFile() in SAT.py to better explain function.
  - Rearrange functions within SAT.py for better organization.
Add Solver object

  - Add Solver.py file which holds the Solver object. Solver object holds operations for SAT object to help solve satisfiability for a set of clauses (of literals) defined by the SAT object. The Solver object is initiated by reading in a CNF file (creating a SAT instance).