Move all k6 config to its own folder

Closes #257 (closed), waiting for !165 (merged) to be merged.

This MR introduces new config folder where we will store Environment, Project, and Options Config files. This change also involves a change to the Dockerfiles and a large update to our docs.

Additional change: the Generator now will import large project only if either it doesn't exist or if its version number doesn't match config in the project's description. Thus version setting was added to the Project Config file.