Migrate xprofilemeta functions to the WP metadata API

The case of XProfile metadata is complex, because xprofile groups, fields, and
data all store their metadata in a single table, differentiated by object_type.
This complication requires additional filters on WP's core metadata queries.

See #4551

git-svn-id: https://buddypress.svn.wordpress.org/trunk@7862 cdf35c40-ae34-48e0-9cc9-0c9da1808c22
Don't run get_user_meta( 'last_activity' ) warning during last_activity mirroring

git-svn-id: https://buddypress.svn.wordpress.org/trunk@7863 cdf35c40-ae34-48e0-9cc9-0c9da1808c22
POT, generated from r7863

git-svn-id: https://buddypress.svn.wordpress.org/trunk@7864 cdf35c40-ae34-48e0-9cc9-0c9da1808c22
Pass $group object to bp_get_group_description_excerpt filter

This allows theme/plugin authors to more easily customize excerpts.

Fixes #5393

git-svn-id: https://buddypress.svn.wordpress.org/trunk@7865 cdf35c40-ae34-48e0-9cc9-0c9da1808c22
POT, generated from r7865

git-svn-id: https://buddypress.svn.wordpress.org/trunk@7866 cdf35c40-ae34-48e0-9cc9-0c9da1808c22