Removed nta git submodule, replaced with CMake commands to manually clone,
fetch, and checkout nupic.core repository.  This also allows overriding the
defaults on the command line via NUPIC_CORE_REMOTE, for the remote repository
url, and NUPIC_CORE_COMMITISH, for the specific sha.
Remove nupic.core entry from .gitmodules
Specify WORKING_DIRECTORY in git fetch
lower-case "set" for consistency
Updated with feedback in numenta/nupic#817
Same result to EXIT_CODE variable
Remove (now empty) .gitmodules file entirely
Config file
Config files and modules files
Merge remote-tracking branch 'DavidRagazzi/config-file' into remove-git-submodule

Conflicts:
	CMakeLists.txt
Merge branch 'remove-git-submodule' into docker-centos