Rewriting adaptive grid

Summary

The class AdaptiveGrid is now a real dune grid, is derived from GridDefaultImplementation and can be used wherever a grid/gridview is expected.

More

Additionally to make AdaptiveGrid a dune grid, I have removed the static instance method. It was necessary, to always create an AdaptiveGrid before any function providing a const Grid& can use it (like the makeGlobalBasis function. Thus, this is the same, as requiring that the user always constructs an AdaptiveGrid. This can be done with a regular constructor. Since then the grid is created and the GridView returns the correct AdaptiveGrid on grid(), the GridView can be directly passed to the ParallelGlobalBasis.

Implications

• The ProblemStat always stores an AdaptiveGrid.
• The DefaultProblemStatTraits define the AdaptiveGrid as Grid
• The ParallelGlobalBasis can be created with any dune grid, including the AdaptiveGrid.
• Automatic adaption is only provided if the AdaptiveGrid is used.
• The user can pass a non-adaptive Grid to ProblemStat, that is automatically wrapped in the AdaptiveGrid class.