Add versioning workaround support for batch actions

* add `can_cancel` flag for progress page, hide button if set
* overhaul populate/refresh/execute to launch socket/subprocess if necessary

tailbone/progress.py

@@ -2,7 +2,7 @@
 ################################################################################
 #
 #  Rattail -- Retail Software Framework
-#  Copyright © 2010-2017 Lance Edgar
+#  Copyright © 2010-2018 Lance Edgar
 #
 #  This file is part of Rattail.
 #
@@ -28,6 +28,8 @@ from __future__ import unicode_literals, absolute_import
 
 import os
 
+from rattail.progress import ProgressBase
+
 from beaker.session import Session
 
 
@@ -43,7 +45,7 @@ def get_progress_session(request, key, **kwargs):
     return session
 
 
-class SessionProgress(object):
+class SessionProgress(ProgressBase):
     """
     Provides a session-based progress bar mechanism.
 
@@ -82,6 +84,3 @@ class SessionProgress(object):
             self.session['value'] = value
             self.session.save()
         return not self.canceled
-
-    def destroy(self):
-        pass