Add translate function to MeshTransformation and Mesh class:

  mesh.translate(p);

Complements existing function mesh.rotate().
Add unit test for mesh translation
Add unary minus operator to Point
Initial sketch of CCFEMFunctionSpace
Compute total dimension of CCFEM space and add accessor function for dim().
Build bounding box trees for all meshes
Add (empty) infrastructure for computing mesh-mesh collisions
Sketching of code for tree-tree collision
Make recursive search functions static in GenericBoundingBoxTree for consistency.
Some of the functions will need to deal with multiple trees.
First implementation of bounding box tree-tree collision
Bug fix in tree-tree collision
Some debugging
Remove a recursive collision function and reuse another.
Does not decrease perforomance noticeably.
Rename Cell::contains --> Cell::collides with copy left of old function
for backwards compatibility.
Add test for triangle-triangle collision
Add out typemap for pair of vectors
Work on entity version of mesh-mesh intersection:
- remove additional mesh argument for compute_entity_foo
- some recursive functions in GenericBoundingBoxTree can be removed
  (next changeset)
Rework implementation of compute_entity_collision
Implement entity-entity version of mesh-mesh collision.
Needs debugging.
Get tree-tree collision detection working. cell-cell test only
implemented for triangle-triangle collisions but will be easy
to extend to 3D (by adding the corresponding test in TetrahedronCell.cpp).