优化工单模块，增加企微模块

sg_wechat_enterprise/we_api/client/api/merchant/common.py

@@ -0,0 +1,17 @@
+# -*- coding: utf-8 -*-
+from __future__ import absolute_import, unicode_literals
+from wechatpy.client.api.base import BaseWeChatAPI
+
+
+class MerchantCommon(BaseWeChatAPI):
+
+    def upload_image(self, filename, image_data):
+        res = self._post(
+            'merchant/common/upload_img',
+            params={
+                'filename': filename
+            },
+            data=image_data,
+            result_processor=lambda x: x['image_url']
+        )
+        return res