Don't treat plain "(c)" symbol or similar as emoji

Even though some plain characters appear in OS X character palette, OS X doesn't render them as emoji by default unless they are suffixed with VARIATION_SELECTOR_16.

This change ensures that the clients using gemoji don't accidentally replace these plain characters with emoji equivalent.

References #56 

/cc @aroben 

P.S. Changes to iron this out in `db/aliases.html` coming in forthcoming pull.