Use document.getElementById rather than $( '#*' )

Because http://jsperf.com/wrap-an-element-or-html-collection-in-jquery

Related: https://github.com/GigaOM/gigaom/pull/5928

See: https://github.com/GigaOM/gigaom/issues/5929
Can `$content_container` and `$content` be combined? `$content_container` never gets used again.
maybe `this.$content = this.$body.find( '.post section.body.entry-content > div' );` ?