Component: Dark's User- and Data- Management

[StachuDotNet]

This issue organizes anything related to the management of Dark's users (Dark developers) and their data. Package code, user code, data, the lifecycle of code, etc.

This is all a bit blocked by us getting the "dark cloud" back up and running.

High-level user operations

• allow users to add their discord names to their profiles, so that we can authenticate them in discord for support. Should be entirely done in Dark (apart from the client side). Literally just a field we store in a DB.
• allow users to change their associated email address
• Add ability to delete user account or "canvas" (see old Support deleting a canvas #2642, Allow deleting accounts #3073)

Source code access and management

• Support contributing to a public canvas (see old Support contributing to a public canvas #2645)
• bring back undo/redo
• batch undos/redo (see old Batch undos #2678)
• Allow adding users to just one canvas
• Implement read-only mode for admins
  • Admins (that is, me) occasionally need to look at canvases to figure out bugs, etc. However, it's very easy to accidentally click somewhere that changes code without realizing it (just now, I accidentally clicking on add new parameter which breaks callers).
  • I'd like to be able to view canvases while being certain I can't accidentally break anything.