Remove the deprecated 'global' methods.

The ReferenceElement class now has a 'geometry' method, which returns
a full-fledged geometry object.  That object, in turn, has a 'global'
method, which is to be used from now on.
Minor improvements to the doxygen output

The \brief description should really be brief, otherwise it looks
stupid in the html output.
Remove deprecated method 'mapping' and corresponding type 'Mapping'

The new method 'geometry' is to be used instead.
Minor doxygen improvement
Remove deprecated Method volumeOuterNormal

The method integrationOuterNormal is to be used instead.
Remove the deprecated method initializeTopology