Model misc changes

See merge request szt-ab-2020212/group-01/shrug!42

Balancing

Closes #86

See merge request szt-ab-2020212/group-01/shrug!41

Resolve "Buildings should be more likely to break down the older they are"

Closes #65

See merge request szt-ab-2020212/group-01/shrug!35

# Conflicts:
#   Assets/Model/Landscape/Building.cs

Document and refactor the view and other improvements

Closes #69 and #84

See merge request szt-ab-2020212/group-01/shrug!38

Document people and related classes

Closes #85

See merge request szt-ab-2020212/group-01/shrug!39

Resolve "Model.Cartography tests"

Closes #45

See merge request szt-ab-2020212/group-01/shrug!37

Fix broken placer reference, add building icons, move some properties from visitable building to building.

Document and refactor UI helper classes and implement help menu functionality with already existing ToggleGroup instead of new code in UIManager.