Removing rabix-common

rabix-common package used to be installed on docker images alongside
tools and wrappers. As wrappers are now deprecated in favor of json
schemas/adapters this package is no longer neded.
requirements conflict resolve
Removing old stuff, figuring houw to integrate new

So far checksum command can work with python 2 and 3. Next goal is to
move executors.cli run logic torabix.cli.
Merge branch 'feature/json-wrappers' of github.com:rabix/rabix into feature/json-wrappers

Conflicts:
	rabix/__init__.py

I'll try to figure out how to do without MAPPINGS global...