Add stockpile/supply-group/paused UIseparators in prodqueue

[Ophiuchus]

Starting from an idea from @alleryn, that en/disabling of stockpile use is clunky and the stockpile using items should be on top of the production queue.

Right now also one use case is really badly supported:
* Refilling stockpile - i need to set most of my production to paused in order to refill it

I think it introducing separators to split the production queue in three parts (stockpile enabled, normal production, paused) would help minimizing micromanagement in combination with imperial stockpile.

What i mean is having two separators you can move around in the production queue similar to production queue entries.
Everything above the top separators gets stockpile use enabled, everything below the lower one gets paused.
This could also be additional to the current right-click en/disable mechanism.

If we dont want something like the separators we should add some support for refilling the stockpile. E.g. a menu option "Pause/unpause all queue items below this one". Or a 1-turn production item "10 PP effort to stockpile" (although I'm not sure if one can do this with the current mechanisms without adding a one turn delay).

p.s.:
Useful historical reading: http://www.freeorion.org/forum/viewtopi ... 852#p90841

[Oberlus]

After thinking about it I really like the idea of the separator (with the second one for paused production I like it even more). It is a powerful yet simple way to manage production queue and stockpile.

[Ophiuchus]

With geoffs suggestion for round four of stockpile this could be simplified to

Normal prio: enabled to draw from stockpile. if you add new production items, they end up at the end of these
Low prio: not enabled to draw from stockpile. (e.g. if you want to refill the stockpile)
No prio: paused