Rewrite language overlay

* Stop copying and pasting HTML into template
* Add serialize function for turning HTML in language list
* Separate language overlay code
* Separate preferred languages code
* Make article title render in the language overlay

Change-Id: Ica241c6ec7743fb5d07240b022d28eb24d9dfac7
Correct left padding on headers and footers in 'list' overlays

On search, talk and language overlays the header doesn't line up
with the list of results. This fixes it.

Change-Id: I78f608b43cc6b9c304fef08cd29edbb250dc21f9
Story 836: Promote language search to stable

Change-Id: Ie44d9e24b2c1449ed112addf0048ed13d812662b
Merge changes Ie44d9e24,I78f608b4,Ica241c6e

* changes:
  Story 836: Promote language search to stable
  Correct left padding on headers and footers in 'list' overlays
  Rewrite language overlay