Build for s2i python images

Release process

e.g. from 0.3-SNAPSHOT to release 0.3 and create 0.4-SNAPSHOT

• set IMAGE_VERSION to new stable version X in Makefile (e.g. 0.3)
• cd build_scripts and run ./build_all.sh and then ./push_all.sh
• Update IMAGE_VERSION to (X+1)-SNAPSHOT (e.g. 0.4-SNAPSHOT)
• ./build_all.sh and then ./push_all.sh
• Update main readme to show new versions of stable and snapshot
• Update versions in docs, Makefiles and notebooks of stable version ./update_python_version.sh X X+1, e.g ./update_python_version.sh 0.2 0.3 (check that any references to X-SNAPSHOT are updated to X - may need manual intervention)
• Update the doc/source/reference/images.md manually with the latest image versions