Automatic train stations (#1353)

## Description:

Train stations are now built automatically when a factory is
constructed.

Changes:
- When a factory is built, nearby structures are connected to the rail
network
- When a city is built near a factory, it is connected to the rail
network
    - All structures behave the same when a train stops: to be defined
    - Removed station badge
    - Gold income is now related to the structure's level

## Please complete the following:

- [x] I have added screenshots for all UI updates
- [x] I process any text displayed to the user through translateText()
and I've added it to the en.json file
- [x] I have added relevant tests to the test directory
- [x] I confirm I have thoroughly tested these changes and take full
responsibility for any bugs introduced
- [x] I understand that submitting code with bugs that could have been
caught through manual testing blocks releases and new features for all
contributors

## Please put your Discord username so you can be contacted if a bug or
regression is found:

IngloriousTom

resources/lang/en.json

@@ -242,7 +242,6 @@
     "atom_bomb": "Atom Bomb",
     "hydrogen_bomb": "Hydrogen Bomb",
     "mirv": "MIRV",
-    "train": "Train",
     "factory": "Factory"
   },
   "user_setting": {
@@ -446,7 +445,6 @@
     "cooldown": "Cooldown",
     "type": "Type",
     "upgrade": "Upgrade",
-    "create_station": "Create Station",
     "level": "Level"
   },
   "relation": {