Simple tech tree

Simple tech tree:

Begin state: `Constyard` produces:
 - `Windtrap`
 - `Refinery`

Upon placing `Refinery`, adds to `Constyard`
 - `Barracks`
 - `Silo (?)`
 - `Light Factory`

Upon placing `Light Factory`, adds to `Constyard`
 - `Heavy Factory`

Upon placing `Heavy Factory`, adds to `Constyard`
 - `Palace`

