TwentyFifteen:
- Fix image caption alignment in the editor.
- Remove unused var from functions.js.
Also includes few images that were shrunk a bit when running grunt precommit.
Fixes #30493.
Built from https://develop.svn.wordpress.org/trunk@30562


git-svn-id: http://core.svn.wordpress.org/trunk@30551 1a063a9b-81f0-0310-95a4-ce76da25c4cd