[WIP] Exponential barrier

[cvanaret]

• [x] Introduce a superclass BarrierProblem of PrimalDualInteriorPointProblem
• [x] Make InteriorPointMethod a template parameterized by the type of barrier problem
• [x] Introduce a class ExponentialBarrierProblem that inherits from BarrierProblem
• [ ] Implement ExponentialBarrierProblem

[amontoison]

@cvanaret I updated GALAHAD and I can test all CUTEst problems with the version of Nick, should I focus on the version of GALAHAD for now or work together on the version in Uno?

[cvanaret]

@amontoison I'll be working on the Python bindings until ICCOPT and I'll get back to the barrier method in August (still need to refactor some stuff before I implement the exp barrier). So you should definitely focus on GALAHAD for now :) Thanks!