Cherry-pick "Merge branch 'DoxygenFixes-master-20190121' into 'master'" into 1.0

Doxygen Fixes, master branch (2019.01.21.)

See merge request !425 (merged)

(cherry picked from commit ccef0bd8)

• ef1c63e0 Now running doxygen in the build directory's runtime environment.
• 1e57ba5e Updated the Doxygen find-modules to work correctly with LCG_94.