Various documentation enhancements.

Mainly:
- added \relates tags to standalone functions
- put all Concrete* classes into grid_internal group (which does not
  figure in the Modules list, on purpose)
- simplified docs of some classes from linalg

Conflicts:

	lib/assembly/discrete_boundary_operator.hpp
Corrected include paths in the generated C++ docs.
Added a search field to the generated Doxygen documentation.
Added a missing include to bempp.swg.
Updated README and VERSION.
Removed an unused file.
Changed version number in documentation to 1.9.
Documentation enhancements.
Added a method creating a grid from connectivity arrays
(suggested by Alexander Eliseev).
Removed Python bindings of dumpblcluster.
Small documentation fixes (grid_factory.hpp).
Ported tutorial_dirichlet.py to the new visualization2 module.
Added licence header to extended_bem_cluster.hpp.