Changes to block descriptions to make building-on-building placement rules more clear

The current system of labelling things as having the quality of Solid or Ground-only is alright, but it's unclear that you:
Can place platforms on pathways, stairways, & power shafts
Can't place dam-related buildings on platforms

I suggest that each building has Requires & Support sections, with the 3 possible options for said fields being:
Light - Most buildings require light, platforms require light and support light
Heavy - Dam-related buildings are heavy and may support heavy, which explains why they can't be placed on platforms
Ground - Only Terrain Block supports ground, mines & Underground Piles require ground

Also, add the quality of Half-block. This means platforms can be placed on the same tile as this building, which would be used for stuff like stairs & power shafts

Some examples:

Dam
Requires: Heavy
Supports: Light

Levee
Requires: Heavy
Supports: Heavy

Metal Platform
Requires: Ground
Supports: Light

Straight Power Shaft
Requires: Light
Supports: None
Half-block