Clean-up in `admin/bp-members-classes.php`:

* Use sprint() on URL's to remove hard-to-read concatenation
* Audit use of get text functions (a few were incorrectly escaped, others incorrectly nesting other functions)
* Fix inconsistencies between single-site and multi-site list tables
* Code formatting, whitespace, etc...

Fixes #5654.

git-svn-id: https://buddypress.svn.wordpress.org/trunk@8438 cdf35c40-ae34-48e0-9cc9-0c9da1808c22