New Watch page header

Update the top of the watch page to explain what the messages are all
about. Text still on the way. Google CSE temporarily removed.

* Describe what watching actually means
* Identify what Church Online is
* Consolidate watch UI
* Keep Church Online visually associated with a series
* Set Church Online with variable, rather than simply "latest"
* New header background image

Changes to be committed:
modified:   _includes/tertiary.html
modified:   _layouts/watch-archive.html
new file:   images/watch/watch-bg-small.jpg
new file:   images/watch/watch-bg-small@2x.jpg
new file:   images/watch/watch-bg.jpg
new file:   images/watch/watch-bg@2x.jpg
modified:   scss/design/_search.scss
modified:   scss/design/_type.scss
modified:   scss/pages/_watch.scss
modified:   stylesheets/app.css
modified:   watch/_posts/2014-03-29-the-counselor.md
modified:   watch/index.html
Update type on watch archive
Update Watch Index headline
Merge watch-index