Zip Builder: generate uniform zip across all build machines

[bgermann]

At the moment the different build machines build plugin zip files with potentially different timestamps. It would be of great benefit to have uniform zip downloads. It does not feel very good to have a download (same URL) containing runnable code that changes depending on which server you get it from.

At ticket:619 I gave some ideas how to do it.

[Otto42]

Duplicate of #619.

Please don't create tickets that are dupes of existing ones, especially when you already know this as a fact. Making the ZIPs shared is slightly complex with the current environment, but the existing ticket has the exact same problem and the same solution, in the long run.