feat: reorganize tech towards housing tiers

[bahrmichael]

• It feels weird to produce milk when I can't use it for anything.
• I want to know what I'm producing e.g. bread for. If my city is not demanding it, why should I research and produce it. This requires knowing what will come, and not just knowing what the current situation is.
• Trains being a prerequisite for multiple towns also feels wrong, that should be a prerequisite for public transportation.

[bahrmichael]

Factorio follows the approach that you research things that are required for higher tier things before you research those higher tier things. Switching it around that you first get higher housing tiers and then have to research the food that they need goes against that direction and may be counterintuitive to someone who already knows Factorio.

Milk production could be moved into its own technology though.

And trains should be a prerequisite for public transportation indeed.

[bahrmichael]

Implemented in v0-2-0