Add auto-indentation for python

[masad-frost]

Adds rules for auto indent using onEnterRules.

Q: I Initially tried using indentationRules but decreaseIndentPattern seemed tricky in python. Any reason to use one over the other?

[alexdima]

indentationRules are much more advanced then onEnterRules. They are used when moving lines, when pressing Tab, when pressing Enter, or when executing commands to re-indent the file. They should describe the indentation rules of a language completely. I don't know a good place where they are documented, perhaps @rebornix knows.

The onEnterRules are simply used when one presses Enter, but are easier to get right.

[masad-frost]

Cool, I played with it a little, and I think I get it. Thakns!