Fixes #70 by activating the proper environment on a macOS machine
This MR proposes the addition of activation/deactivate scripts to bob-devel to tackle the missing setup of variables required to compile packages on a mac machine.
These are the variables which are activate/deactivated:
MACOSX_DEPLOYMENT_TARGET(set to 10.9 by default)
CONDA_BUILD_SYSROOT(which gets incorrectly set to the latest SDK path)
SDK_ROOT, to the same value of