Feature: jump to match on click

[paulirish]

On clicking a range, it will scroll the page to reveal its matched item (between source and generated)

Two smaller edits added to help facilitate this:

• text will wrap so all the source is onscreen without overflow
• hint added to tell user about drag 'n drop

[paulirish]

@sokra you're a busy guy, but if you have time to look at these PRs, i'd appreciate it

[sokra]

Thanks