More work on using hlib matrices for bem in oomph-lib

Still not working, I think the problem is due to a permuation of the matrix
added by hlib somewhere...
Use analytic bem integration by default if possible

and fix parameter -use-numerical-bem so that does what it should!
Speed up selection of node order going into Lindholm formula

* Nodes need to be in order s.t. the normal gotten by Lindholm
  is in the right direction.

* Used to do this by brute force (calculate both normals, if not correct
  then swap nodes).

* Now do it by checking the sign of Normal_sign

* Also slightly improve error message for normal not a unit vector
Fix ordering problems in H-lib matrices

* Needed to have nodes within triangles in particular order

* Self test still not great:
** could do with measuring eigs? or something other than fpdiff(matrices)
** test for more parameters (in particular something more hierarical)
** more/bigger meshes
** where is the extra *-1 coming from?
** fix ordering of input/output from H matrix multiply