About page updates.
 * Live-update the number of active translations.
 * Finalize most strings.
 * Lazily remove links to admin-only screens based on cap checks.

Merges [30840] and [30841] to the 4.1 branch.

see #30435.

Built from https://develop.svn.wordpress.org/branches/4.1@30858


git-svn-id: http://core.svn.wordpress.org/branches/4.1@30848 1a063a9b-81f0-0310-95a4-ce76da25c4cd
About page design for 4.1.

Merges [30857] to the 4.1 branch.

props melchoyce and ryelle, who again outdid themselves.
see #30435.

Built from https://develop.svn.wordpress.org/branches/4.1@30859


git-svn-id: http://core.svn.wordpress.org/branches/4.1@30849 1a063a9b-81f0-0310-95a4-ce76da25c4cd