Strip ST, LT, UT in AppendValueToUTF8String.
Strip ST, LT, UT in AppendValueToUTF8String.

In all other places in the code, trailing spaces were stripped from
values with these VRs.  Do the same in AppendValueToUTF8String().

dgobbi/vtk-dicom,dgobbi/vtk-dicom,dgobbi/vtk-dicom