don't use nonstandard window.location.origin in customizer JS; fixes #11317
Merge pull request #11336 from twbs/fix-11317

don't use nonstandard window.location.origin in customizer JS
Removed duplicated class change from migration instructions
Merge pull request #11345 from pborreli/patch-3

Removed duplicated class change from migration instructions
Fixed links

Links to same-page anchors were treated as external links.
Merge pull request #11354 from Ore4444/patch-1

Fixed links
Merge branch '3.0.0'