Refactoring the Dirichlet and the Neumann boundary conditions.

Min. interations feature was fixed in the GMRES method.
Timers for explicit and semi-implicit timestepping were added.

Adding new classes - AnalyticSolution, NeumannBoundaryCondition, DirichletBoundaryCondition, LinearDiffusion, RightHandSide, TimeFunction, ZeroRightHandSide
Updating classes (implementation of partial derivations) - SinWaveFunction, ExpBumpFunction, SinBumpsFunction
Updating classes (modifying and adding new methods) - SimpleProblemSetter, SimpleProblemSolver
Modifying - simple-solver.cfg.desc