Messages: soft-deprecate existing autocomplete CSS/JS by moving assets into deprecated folder.

Functionality hasn't been changed, the scripts have just been moved. Eventually, these will be
replaced by a newer auto-suggest JS/UI, then these will be used just for backwards compatibility
with old themes.

See #3278 and #5735.


git-svn-id: https://buddypress.svn.wordpress.org/trunk@8559 cdf35c40-ae34-48e0-9cc9-0c9da1808c22