Settings for more control over special deal prices

[fenhl]

Proposing as an alternative to #1899. Instead of arbitrarily using the betavariate distribution for some price ranges and the uniform distribution for others, this PR adds settings to control the price range and distribution individually. As a bonus feature, I've also added an option to have each special deal location use the price of its vanilla item. Something like the features suggested in the comments of #1987 could be implemented as another option of this setting.

[cjohnson57]

I think this is the kind of thing I'd rather leave as a plando-only feature... This level of control over something so specific feels like GUI bloat

[fenhl]

I'm not sure if it's possible to add this functionality for plando while keeping the current interface for GUI settings. Might have to move this feature outside settings to achieve that. Will have to give it some more thought.