DOC: Rename DCMTKException DCMTKExceptionOrErrorReturn

The original name DCMTKException wasn't explicit enough about how the macro behaves
which is to conditionally throw an exception based on a default argument to
functions in which it appears.

Change-Id: I99704495685a1d1040b5c0f9b13a91f6e061c47a
Merge topic 'DCMTKExceptionVerbosity'

9376e3b DOC: Rename DCMTKException DCMTKExceptionOrErrorReturn