Allow manual repartitioning in distributed tria

Allow manual repartitioning in distributed tria

A new flag no_automatic_repartitioning in
parallel::distributed::Triangulation will disable the automatic
repartitioning when calling execute_coarsening_and_refinement() (or
things like refine_global(), ...), resulting in all cells staying on the
processor they were before.

A function repartition() will execute the repartitioning resulting in
the same as the old behavior. Splitting the process of refining and
partitioning into separate functions allows for advanced techniques when
handling several meshes at once.

Added tests that check that attaching and transfering data is working
correctly.

Resolves #673.