Extract logging from GMGPolar class

[EmilyBourne]

The GMGPolar class contains lots of logic that is only useful for debugging or testing. Namely:

• print statements
• code related to the exact solution

Currently these objects are excluded using if (verbose). The presence of an exact solution is known at compile-time so it is a shame to check this dynamically repeatedly over the course of a simulation.

I think everything related to exact_solution_ can be extracted to a separate class and only used for testing. The only thing preventing that currently is that exact_solution_ is used in the printing. I see 2 possible solutions for this:

1. Change the format of the print output so the things related to the exact solution are printed on a separate line that can be handled with the exact_solution_ object
2. Add a logger class that can take different forms depending on the requirements of the simulation, e.g.:
   • Empty logger, no output
   • Output to log file/cout
   • Ouptut with/without exact_solution_ information