Bug 173114

In Issue #161700, a problem has been brought up that users typically find themselves typing at the last visible line in
the editor, thus not seeing the entire context of the piece of code they are working at. A small part of the problem has
been fixed there (users are now allowed to manually scroll so that end of the file is not at the last visible line), but
in most situations, when editing somewhere close the bottom end of the visible area and adding more lines, users still
find themselves typing at the last visible line unless they manually scroll down. 

What would solve this problem is *automatic* scrolling before reaching the end of visible area. Imagine I manually
navigate to 3rd visible line from the bottom, hit enter to create a create a new line and start typing. Instead of the
text staying and the active line moving down (after hitting the enter key), the editor would behave as if 3rd line was
the last visible line - text would scroll and active line would remain on 3rd visible line from the bottom. Thus, I
would still see 2 lines beyond the text I'm typing.