Feature - Make Stackable factories have a benefit

**Describe the bug**
the factories don't actually stack. the structure itself does but they don't produce more money per train, nor do they produce more trains. the income of the trains is also not scaled by the city or port stack size.

**To Reproduce**
Steps to reproduce the behavior:

1. place as many factories on a stack near some cities or ports and compare the income to a single factory.

**Expected behavior**
when a city, port, or factory has a stack, the trains should have more value.

**Desktop (please complete the following information):**

- OS: windows but isn't this a web based game?
- Browser: opera gx (chromium based)
- Version: 25

**Additional context**
Add any other context about the problem here.