Collaboration-friendly workflow / Savefile format

[marcos-diaz]

• It is PREFERABLE that the solution have meanings to collaborate effectively.
• It is PREFERABLE that multiple people is able to work in the same model in parallel (without overwriting each other).
• It is PREFERABLE that users are able to do pair-review of changes before these are merged.

(Basically what we need is textual (non-binary) savefile format such as xml or json. So it can be integrated in the common GIT developer workflow.)