Add rangy library (MIT license)

Rangy is a cross-platform library for managing text ranges, selections,
and so on, which can also apply a highlight to any range, automatically
adding the appropriate <span> elements where needed. We'll be using it
for the text-highlighting feature on the question page.

The version checked in here is the latest currently available, 1.3a772,
released in February 2013. I chose the 1.3 alpha release instead of the
stable 1.2 release because rangy's highlighter module is new in 1.3.
Text selection now works properly

Several changes in this commit, which go together as a logical unit:
  * Moved new-answer edit control to top of question pane
  * Added "scripture-quote" CSS style
  * When user highlights a section of text, it will show up in the
    question pane in "scripture-quote" style
  * When answers have a (non-blank, non-null) textHighlight value,
    the selected portion of Scripture will also show up above the
    answer, again in "scripture-quote" style