Change admin language pack selection dropdown
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Change the language pack download selection dropdown in `/update/languages` so
that it uses the more arbitrarily stylable Bootstrap components, instead of
`select` and `option` elements. See:
http://getbootstrap.com/components/#dropdowns
Also improved readability of some JS by giving more sensible function names and
through judicious user of jquery instead of `sprintf`ing html elements.
Included a placeholder image to signify beta language packs.
Change beta image to text
Revert an unintended change
Merge pull request #2791 from MCGallaspy/issue-2720

Change admin language pack selection dropdown