Modify the include path and the copy path settings
Refactor the TopDirectory variable and the exports
Missed  Replacement
Get rid of SURGSIM_TOP_INCLUDE_DIR

also get rid of extraneous include_directories entries
Merge branch 'feature/addsubdirectory-cmake' into 'master'

Enable OSS to be built in concert with external projects

+1: Ryan Beasley, Julien Lenoir, haizhouW

Merged-on: https://www.assembla.com/code/OpenSurgSim/git/merge_requests/1031914