Solve LP relaxation at end of FPR

[StevenMaio]

The final step in FPR is solve the LP relaxation after the integer variables have been fixed.

• [x] solve LP at end
• [ ] think of ways to save solution
• [ ] add a unittest to see what happens in the case of infeasibility

[StevenMaio]

The bulk of this is done. One thing to consider is how should we store the solution?