Add 'Unattached' filter for galleries.

props pento.
fixes #29329.
Built from https://develop.svn.wordpress.org/trunk@29722


git-svn-id: http://core.svn.wordpress.org/trunk@29496 1a063a9b-81f0-0310-95a4-ce76da25c4cd
Don't display Edit links for attachments user cannot edit.

props skaeser.
fixes #29596 for trunk.
Built from https://develop.svn.wordpress.org/trunk@29723


git-svn-id: http://core.svn.wordpress.org/trunk@29497 1a063a9b-81f0-0310-95a4-ce76da25c4cd
Avoid PHP notices in media modal caused by orphaned attachments.

fixes #29566 for trunk.
Built from https://develop.svn.wordpress.org/trunk@29724


git-svn-id: http://core.svn.wordpress.org/trunk@29498 1a063a9b-81f0-0310-95a4-ce76da25c4cd
Make sure we're on the media grid page before calling wp.media().

props azaozz.
fixes #29520 for trunk.
Built from https://develop.svn.wordpress.org/trunk@29725


git-svn-id: http://core.svn.wordpress.org/trunk@29499 1a063a9b-81f0-0310-95a4-ce76da25c4cd
Merge pull request #12 from WordPress/master

Update