Twenty Fifteen: correct styles for color schemes

Props iamtakashi, fixes #29976.



git-svn-id: https://develop.svn.wordpress.org/trunk@29971 602fd350-edb4-49c9-b593-d223f7449a82
Twenty Fifteen: beautify the header in IE 8.

Props afercia, fixes #30042.



git-svn-id: https://develop.svn.wordpress.org/trunk@29972 602fd350-edb4-49c9-b593-d223f7449a82
Twenty Fifteen: correct button sizes.

Props iamtakashi, fixes #30045.



git-svn-id: https://develop.svn.wordpress.org/trunk@29973 602fd350-edb4-49c9-b593-d223f7449a82
Twenty Fifteen: correct comment meta alignment when avatar display is turned off.

Props iamtakashi, fixes #30046.



git-svn-id: https://develop.svn.wordpress.org/trunk@29974 602fd350-edb4-49c9-b593-d223f7449a82
Twenty Fifteen: Adding in the twentyfifteen credits action.

Props iamtakashi, fixes #30051.



git-svn-id: https://develop.svn.wordpress.org/trunk@29975 602fd350-edb4-49c9-b593-d223f7449a82
Twenty Fifteen: updated styles for skip link.

Props afercia and iamtakashi, fixes #30043.



git-svn-id: https://develop.svn.wordpress.org/trunk@29976 602fd350-edb4-49c9-b593-d223f7449a82