* Moves some admin only functions into wp-admin/includes/ms.php from wp-includes/ms-functions.php
* Reworked the variable naming to be more in line with the Coding Standards
* Introduced a new get_space_used() function instead of calculating it in multiple places.
Fixes#21181 props dllh and jkudish for inital work on this.
git-svn-id: https://develop.svn.wordpress.org/trunk@21387 602fd350-edb4-49c9-b593-d223f7449a82