DOC: Update documentation graph font to avoid warnings

Recent versions of Doxygen do not include the FreeSans font for use in
generating graphs, and default to Helvetica anyway when FreeSans is not
found. By specifying Helvetica in the configuration file, a warning is
fixed.

Change-Id: I2991416c3dcb958709df928ad929694711c85b25
DOC: Move an included STL file out of the itk namespace

In addition to being bad practice, this fixes a Doxygen warning.

Change-Id: Ia3bbc116760b8f49d356166dc9ec19abe51ca4d9
Merge topic 'DOT-Font'

e5c9a2a DOC: Update documentation graph font to avoid warnings
Merge topic 'Doc-include-warning'

a3f5e69 DOC: Move an included STL file out of the itk namespace