Task sub split

Merged Matthieu Schaller requested to merge task_sub_split into master

This implements #175 (closed) While at it I also removed some dead code (including #174 (closed)) and cleaned up the linking of libraries in the Makefile. For some reasons we had still blas in lapack in there.

Finally I have also removed some commented-out old gravity stuff. That should make the diff for the gravity branch much easier to read when it becomes time to merge that in.

Merge request reports