Twenty Thirteen: masonry widgets layout is not updated in the customizer

[celloexpressions]

wp.customize.selectiveRefresh is not defined where the theme's functions.js checks for it, preventing the masonry footer widgets layout from updating properly when widgets are added, deleted, or reordered. This broke sometime between when the change was made to the theme and 4.5.3, and is likely due to the sequence of scripts loading.

See ​https://wordpress.slack.com/archives/core-customize/p1468779925000003, which has a fix from @westonruter. We also need to update the code in ​https://make.wordpress.org/core/2016/03/22/implementing-selective-refresh-support-for-widgets/ as themes may still be copying that.

[celloexpressions]

Bump script version

[celloexpressions]

37390.1.diff​ looks good to me, with the addition of a version bump on the script to ensure that it isn't cached.

[westonruter]

In 38083:

Twenty Thirteen: Fix selective refresh of Masonry-laid out widgets by deferring initialization until DOM ready.

This ensures that the wp.customize.selectiveRefresh object will be available when in the Customizer preview.

Fixes #37390.
Props westonruter, celloexpressions.

[celloexpressions]

Intended functionality resolved.