Makes group avatars not dependant of xprofile component settings

Avatar uploads setting is by default attached to xprofile settings. In case this component is disable and groups component is active, the avatar uploads setting will be attached to groups in order to keep on allowing avatar uploads for groups.

Fixes #5330

git-svn-id: https://buddypress.svn.wordpress.org/trunk@7743 cdf35c40-ae34-48e0-9cc9-0c9da1808c22