Add additional role changes to bp_groupblog_upgrade_user().

* Account for banning and removing users.  Switch these user's roles to
  'subscriber'.
* Remove bp_groupblog_remove_user() hooked to 'groups_banned_member' as the
  parameters did not match.

Conflicts:
	bp-groupblog.php
Fix blog roles on group promotion / demotion.

* Add logic to bp_groupblog_upgrade_user() to account for promotion / demotions
* Remove $blog_id global in bp_groupblog_get_user_role().  Was interfering with
  getting the true blog ID for the user.

Also:

* Deprecate $user_login paramter in bp_groupblog_get_user_role().  Was not being
  used in the function.

Conflicts:
	bp-groupblog.php