[core][cs] change namespace core_dispatch to namespace core_detail;
for non-Cartesian CS's do not derive from core_detail::coordinate_system_units,
but rather use core_detail::coordinate_system_units to define the units type;
[core][cs] update copyright header; make coordinate_system_units a struct;
[geometries][point] update copyright header; replace derivation from CoordinateSystem
by a private typedef (this provides the necessary type checking for the units for
non-Cartesian coordinate systems);
[geometries][concepts][point concept] replace boost::ignore_unused_variable_warning()
by boost::ignore_unused(); add typedef for the units of the coordinate system (this
enables a static check for the units type used in non-Cartesian coordinate systems);
[geometries][concepts] add helper class that provides the type of the
units for non-Cartesian coordinate systems, and sets this type to void
for Cartesian ones (used for type checking in the point class and the
point concept);