First pass at changing Suggestions API approach

Uses classes per @boonebgorges’ suggestion on trac.
Not tested yet.
Fix some PHP parse errors
Tests: stop manually resetting `$bp->avatar` between tests.

This causes tests to fail if those tests call `friends_add_friend()` inside `setUp()`
as the `$bp->avatar->show_avatars` property is unset. Instead, rather than manually
resetting the variable, we'll let `bp_core_set_avatar_globals()`, via `bp_setup_globals`
in `assertPreConditions()`, reset it correctly.

Fixes #5727

git-svn-id: https://buddypress.svn.wordpress.org/trunk@8555 cdf35c40-ae34-48e0-9cc9-0c9da1808c22
Merge branch 'master' into suggestions
Fix some typos

Tests are still failing
Fix copy pasta in filter names
Fix group username query

If group_id isn’t set, BP_Group_Member_Query will add “AND u.ID IN (0)”
to the query, which will break it, so we switch it back to the base
BP_User_Query.