Also print information for time 0

Also change its default from 1e6 to 1e5 and treat it as size_t

The solvers for u0/a0 and v now each have parameters tolerance,
maximumIterations, verbosity

* Merge three files into one
* Merge two functions into one (*_bisection is gone)
* Move linear term out of the nonlinearity
* Use DirectionalConvexFunction from dune-tnnmg

problem_rhs_initial -> accelerationRHS

problem_rhs         -> velocityRHS
problem_iterate     -> velocityIterate
problem_AM          -> velocityMatrix