Fix demand at News Events not being used

[impaktor]

Demand mechanics was never ported into News Event module, thus when there's a large demand for something at a station, the demand could still be very low, preventing player from selling. Also, we don't want to accumulate price/stock/demand at each "OnDock" event.

EDIT: I'll open this as WIP, for feedback, the first and last commits, that both attempt to fix the above bug should be squashed, as first does it wrongly, I believe.

Also I've added a debug tab, which allows generating (random) news. Usually news only spawn +6 months into the game, and only when jumping / in hyperspace.

[impaktor]

I've tried it with both "sold out" and "surplus" event, and note price/stock/demand is modified when docking, and reset when undocking.

Demand is linearly returning to normal as the event closes it's (hidden) deadline. That is one way to solve a problem that has been bothering me: how does the player know when to stop filling up cargo with X and fly to "event system"? This gives a clue. (Perhaps price & stock should also linearly return to normal.... oh well)

I've also tested it with illegal goods. (I realize news event is a good at finding where to buy illegal goods. if the event is for e.g. battle weapons, it will cause a shortage in some system where those are a legal commodity. I had forgotten that was how it worked)

...then I did a rebase. That should not have messed up anything.