Feature/remove vintage treepaths

This MR (based on !18 (merged)) removes DynamicTreePath, MutableDynamicTreePath, MakeableDynamicTreePath, TreePathType::mostlyStatic, and TreePathFactory. None of them is used any more in dune-typetree and dune-pdelab when applying the modernization of the tree traversal algorithms in !18 (merged).

The key is, that the modernized tree traversal only uses HybridTreePath which nicely does the job. The only other remaining tree path implementation is the fully static TypeTree::TreePath. Getting rid of this one is harder, because TreePath<i...> is used heavily as template parameter in dune-pdelab.

Notice that I'm not sure if removing all those implementations without deprecation is a good idea. Hence this MR mostly serves for demonstrating how this could be cleaned up. However, if the removed stuff is considered internal, one may consider merging directly (after !18 (merged) of course).