Issue #2151089 by longwave, joelpittet, c4rl, IshaDakota, pplantinga, gnuget, jeanfei, sbudker1, Cottser: Convert theme_admin_block() to Twig.
Issue #2151095 by joelpittet, longwave | Cottser: Convert theme_admin_page() to Twig.
Revert "Issue #2151095 by joelpittet, longwave | Cottser: Convert theme_admin_page() to Twig."

Sorry, wrong commit credit.

This reverts commit d1653fd046cc53b1a3a2bafe5868cf7ca98a32b5.
Issue #2151095 by joelpittet, longwave, c4rl, IshaDakota, pplantinga, gnuget, jeanfei, sbudker1, Cottser: Convert theme_admin_page() to Twig
Issue #2166529 by Kartagis: Typo in install.core.inc comments.