Add context titles to context_refs

Context titles may be helpful in understanding diffs showing buggy data changes
and may soon be useful again. Furthermore, context titles can reasonably be
expected to be unique. Otherwise they would be highly confusing elements of
the UI since they would require some other means of differentiation.

Signed-off-by: Matt Helsley <matt.helsley@gmail.com>
Signed-off-by: Darren Hart <darren@dvhart.com>
--

xmlstore.py

@@ -136,7 +136,7 @@ def save_task(self, task):
             debug("saving contexts")
             for c in task.contexts:
                 debug("referencing context: %s" % (c.title))
-                self._simple_element(x, "context_ref", {"id":str(c.id)})
+                self._simple_element(x, "context_ref", {"id":str(c.id)}, c.title)
             self._simple_element(x, "complete", {}, complete_str)
             x.endElement("task")
             x.endDocument()