Versioning system for Models / Pages / Workflows (and others?)

[JFQueralt]

Rationale: It would make a lot of sense to have some sort of versioning system for a number of objects in the platform such as

• Models
• Pages
• Workflows
• Settings

Case scenarios:

• Being able to undo a Module, Page, Workflow or set of Settings to a previous state easily.
• Share those differentials from version to version via export.

Further comments: To keep it short (further rationale can be given if requested), I see potential to connect Corteza with a Git, say Github, to keep some transactions reflected on a repo in the form of Issues. Such approach could actually take care of this.