Twenty Fifteen: Final RTL, editor-style, and search padding fixes.

Merges [30953], [30955], [30956] to the 4.1 branch.

Props iamtakashi, alex-ye.
fixes #30744, #30739, #30746.

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Update individual term caches in `get_terms()`.

Merges [30954] to the 4.1 branch.

props boonebgorges.
fixes #30749. see #21760.

Built from https://develop.svn.wordpress.org/branches/4.1@30959


git-svn-id: http://core.svn.wordpress.org/branches/4.1@30947 1a063a9b-81f0-0310-95a4-ce76da25c4cd