[python] generate static methods as real python static methods (closes #2943)

Source:
```haxe
class Main {
    static var a:Int;
    static function main() {
    }
}
```

Before:
```python
class Main:
	pass
def Main_hx_empty_init (_hx_o):
	pass
Main._hx_empty_init = Main_hx_empty_init
Main.a = None;
def Main_statics_main():
	None
Main.main = Main_statics_main
```

After:
```python
class Main:
	a = None

	@staticmethod
	def main():
		None

	@staticmethod
	def _hx_empty_init(_hx_o):
		pass
```