Allow some HTML in the copy of the latest activity update displayed in member header

We pass the saved value through the activity-specific kses filter, which
contains a whitelist of allowed tags. This makes for a more consistent
experience.

Fixes #3374

git-svn-id: https://buddypress.svn.wordpress.org/trunk@8351 cdf35c40-ae34-48e0-9cc9-0c9da1808c22