Store a history of previous project generations

[jbilcke-hf]

Inside the project dir, we should have a "history" tab to brow past models (for this project)

this should be a global tab (in the left tab menu)

that way we could generate a new model while still keeping the previous one

or preview all our past models

[jbilcke-hf]

I have started working on UI to handle multiple projects, but this is far from being finished yet (this isn't a high priority right now)