close_window and new_window command closes #88, #90

Ok I've implemented `close_window` and `new_window` command both as `ApplicationCommand` and `WindowCommand`(as discussed [here](https://github.com/limetext/lime/issues/90)) it's a bit odd but appears that this is how sublime text works.
btw I am not sure about the `IsChecked()` method, how should this method work on commands like `new_window` or `close_window`.
This isn't correct, remember that a buffer can be shared between multiple views i.e. viewing the same file in split view side by side . ```v.Close()``` should be used instead to go through the proper event chain which calls ```on_pre_close```, ```on_close``` etc. I think ```View.Close``` in turn currently faulty calls ```v.buffer.Close()```, but that's for a separate issue number if one doesn't exist already.

BTW, to check out what ST3 does I just created this plugin and ran the "close_window" command and I got the prints for each view I had in that window:
```python
class MyEvListener(sublime_plugin.EventListener):
	def on_pre_close(self, view):
		print("on_pre_close")
	def on_close(self, view):
		print("on_close")
```

Also note that if a file is unsaved and shows the "buffer was modified, do you want to save"-dialog (which IIRC it always does as the mechanisms for that aren't reset after loading a file) and presses "cancel" the close_window/view.Close operations should be interrupted. We can open up a separate issue number for that though if you'd like.