Limit autocomplete to 25 results

I'm not totally sure why we didn't do this years ago, but this fixes
performances problems in the new React tags box, and should improve
autocomplete performance generally in large libraries.

components/zotero-autocomplete.js

@@ -211,6 +211,8 @@ ZoteroAutoComplete.prototype.startSearch = Zotero.Promise.coroutine(function* (s
 			sql += "ORDER BY value";
 	}
 	
+	sql += " LIMIT 25";
+	
 	var onRow = null;
 	// If there's a result callback (e.g., for sorting), don't use a row handler
 	if (!resultsCallback) {