Pass line number in EditScreen URL tokens

The line number should be part of the token, not a static field.
This allows the line to survive through a sign-in redirect.

Refactor the scroll-to-line feature from SideBySide into a common
Java based utility method on the CodeMirror instance. There is no
reason for this to be in pure JavaScript.

Change-Id: I2f1655e5a7c52bc27cc3a987e44210833d8b68bd
5 files changed