Fixing UI data pipe line, re-rendering:
- store section DOM Elements in gr-diff-builder
- find diff section by line range
- store collapsed lines as gr-diff-group
- update gr-diff-builder's data model on expanding collapsed lines
- .right/.left CSS classes applied to td.lineNum instead of .content
Feature: Issue 3910
Change-Id: Ia0cb78aa00cfd910d186a37631fe71a89204a843