Implemention of slack import feature.

web/react/utils/utils.jsx

@@ -982,3 +982,12 @@ module.exports.getUserIdFromChannelName = function(channel) {
 
     return otherUserId;
 };
+
+module.exports.importSlack = function(file, success, error) {
+	formData = new FormData();
+	formData.append('file', file, file.name);
+	formData.append('filesize', file.size);
+    formData.append('importFrom', 'slack');
+
+	client.importSlack(formData, success, error);
+};