Add additional hooks in the registration template.

This will allow theme and plugin devs the opportunity to insert markup
inside the account, profile and blog details sections.

Previously, hooks were available before and after these sections, but
not inside the actual block.

Fixes #5081.

git-svn-id: https://buddypress.svn.wordpress.org/trunk@7475 cdf35c40-ae34-48e0-9cc9-0c9da1808c22