Add documentation to boundary conditions
Correct DirichletBC::fillBC to use column basis for solution

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

Added init-finalize also for vectors.
Require gather/scatter operations instead of direct vector/matrix access.
Rewritten the interpolation.
Added ParallelIndexSet and DOFMapping to be used also in other backends.

Müller, Felix authored Jun 14, 2019 and Praetorius, Simon committed Jun 14, 2019

Changed ISTL solver interface to use parallel solver; Added empty communicator for sequential use of parallel solvers

Removed the direct solver specialization ofr double types in favour of the separate initialization in the creators