Update to Drupal 7.58 for SA-CORE-2018-002

Getting ready for tomorrow's release:

https://www.drupal.org/psa-2018-001

I think for this one, we're gonna be a little tricky and just update core, without including any of the updates to the panopoly_* modules since the last release. That create some temporary "version dissonance" (Panopoly 1.52 will have panopoly_* 1.51 modules in it) but I think that's acceptable for such a critical release.

Anyway, we'll push this as soon as possible after the SA!