Simplify which folders are used

[AntonOsika]

This will let folder structure look like so:

- .gpt_eng
  - archive
  - memory
- prompt
- [all the generateed code files ("workspace") stored on the top level]

It will also stop archiving the workspace – think we should instead version control all the project code via git and let gpt-engineer make commits directly after it generates something.

Waiting to merge until we have a good way to "merge in" the generated code into the existing code: #650

[AntonOsika]

Holding off to merge this until #650 .

After this, we should do #665

[ATheorell]

I believe this is obsolete now that #749 has been merged