Fix: apply excludes for user aliases in user selection view

 - fixes a missing reassignment to the new named variable causing the selection of group aliases to fail in the user selector view of private messages
 - apply the list of excludes when a user selects a group alias to prevent double selection of users already in the list and selection of oneself
Merge pull request #1988 from ligthyear/fix-system-group-aliases

Fix group aliases causing private messages to not be created