unified workshop requests interface

[lstrzebinczyk]

There seems to be a pattern emerging, where I would like to have 3 kinds of request setting in workshops:

• produce some items right now (for example, give me one table)
• try producing items up to a limit (for example, make sure there is always at least 5 cooked fishes in storage
• produce indefinitely (for example, always go fishing)

This needs to be nicely thought through and implemented in acceptably global manner, so that I can use it in many places.