About page, text only (not released for translation), first pass.

Design and finalized text to follow. This is just for the RC crowd.

props johnbillion, helen, markjaquith, nacin.
see #30435.


git-svn-id: https://develop.svn.wordpress.org/trunk@30821 602fd350-edb4-49c9-b593-d223f7449a82
Rename `(get_)the_pagination()` to `(get_)the_posts_pagination()` for clarity.

See #29808
Props obenland


git-svn-id: https://develop.svn.wordpress.org/trunk@30823 602fd350-edb4-49c9-b593-d223f7449a82
Switch to `(get_)the_posts_pagination()` in Twenty Fifteen.

See #29808
Props obenland


git-svn-id: https://develop.svn.wordpress.org/trunk@30824 602fd350-edb4-49c9-b593-d223f7449a82