Iterative solver cleanup

This MR removes duplicate code in iterative solvers by moving

• convergence check
• invalid defect norm check (inf or NaN)
• output

to a class Iteration. A instance of this class is created with IterativeSolver::startIteration and is intended to be kept in the local scope of the apply method. During iteration the method Iteration::step checks for all the things mentioned above. The destructor fills all fields of InverseOperatorResult and prints the final statistics if verbose is positive.

added 2 commits

• 7a80d0a0 - set the solvername by a virtual function
• 9bf611b8 - forbid copying of Iteration and define move ctor

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added 1 commit

• 27930350 - remote startIteration method from IterativeSolver and create Iteration directly

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added 1 commit

• 697abde5 - remove startIteration method from IterativeSolver and create Iteration directly

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resolved all discussions

mentioned in issue dune-common#158 (closed)

added 1 commit

• 0af31d3a - change return type of `IterativeSolver::name()` to std::string

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resolved all discussions

added 1 commit

• 24a802f1 - call Preconditioner::pre before computing the residuum, since pre might change

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@nils.dreier since dune-common!659 (merged) got merged a while ago, it would be nice to use className instead of all the explicit name() implementations.

Besides this, I'd like to merge this soon...

added 53 commits

• 24a802f1...a5cbbad0 - 51 commits from branch core:master
• a337dc31 - Merge remote-tracking branch 'origin/master' into iterative_solver_cleanup
• 93340a73 - use className for determining the name of a IterativeSolver

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added 6 commits

• 93340a73...14d12ed3 - 5 commits from branch core:master
• 19e4e75e - Merge branch 'master' into 'iterative_solver_cleanup'

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merged

mentioned in commit 6cc6544d

mentioned in merge request !334 (merged)

mentioned in commit 9e5267ef