Major changes:
  Add wrapper class AdaptiveGrid<Grid> to be used instead of a
    dune-grid within AMDiS. This provides most of the grid interface
    and supports automatic updates of bases.
  Change: MeshCreator now returns an AdaptiveGrid
  Change: ProblemStat uses AdaptiveGrid internally and returns an
    object of that type
  Add class ParallelGlobalBasis<Basis> as a replacement for a
    dune-functions basis. This implements the complete interface and
    can be used as a replacement for a regular basis in all contexts.
    It supports automatic updates.
  Add free function makeGlobalBasis to make a ParallelGlobalBasis
  Change: AMDiS basis creators now return a ParallelGlobalBasis
  Change: ProblemStat uses ParallelGlobalBasis internally and returns
    an object of that type
  Add classes Observer/Signals. Classes can derive from those to take
    part in the automatic update feature.
  Add update(Event const& e) methods to classes using the feature
    above. They implement the action to be done when the registered
    Event is triggered.
  Remove GridTransfer[-Manager] and replace with the new
    Observer/Signals implementation
  Change: linear algebra communicator is now a part of
    ParallelGlobalBasis
  Add wrapper for DataTransfer objects that can be used instead of a
    base class pointer and performs deep-copy operations on copy
    construction and assignment
  Change: DOFVector DataTransfer member is now stored using the new
    wrapper class DataTransferWrapper
  Change: preAdapt, adapt, postAdapt callbacks are now called after
    calling the respective grid function. Classes that previously used
    any of them had their methods changed accordingly.

Minor changes:
  Remove Comm argument for ctor of [Bi-]LinearForm, DOFVector
  Change ctor argument from Comm to Basis in
    linearalgebra/<impl>/[Matrix-, Vector-]Backend.hpp
  Simplify DOFVector copy/move by defaulting
  Remove DOFVector::resize override
  Remove DOFVectorInterface.hpp
  Change: linearalgebra/Traits.hpp includes the backend-specific
    Traits file. This is required to break an include loop.
  Add global 'solver category' initfile parameter used by the ISTL
    backend communicator when no parameter  at prefix + '->category'
    is found
  Fix commented out parts in DOFVectorTest, DiscreteFunctionTest
  Add unit test for Observer functionality
  Add helper function wrap_or_share (see amdis/common/SharedPtr.hpp)
  Fix backend = ISTL check for ISTLCommTest in CMakeLists