Adjustment of Productive trait

Nerfs: +1 Hammer on 4 hammer tiles, as opposed to 3 hammer tiles.
Buffs: +1 happiness with levee, and production multiplier now applies to
industrial parks as well. (As if anyone ever builds industrial parks...)
XML tidying, Bombardier nerfing

Re-ordered buildings and units in the XMLs to make the build screen
in-game seem more logical. Also, reduced the amount of collateral damage
that Bombardiers can deal.