R1:3f0ffaa9ebc6

Pholio - make create stories include the mock description, if there is one.

Summary:
This diff accomplishes this task by adding an arbitrary metadata store to PhabricatorObjectHandle. This seemed like it would be "necessary eventually"; for example if / when we decide we want to show images in these stories we'd need to add some more arbitrary data. A point of debate is this technique will yield the _current_ data and not the data at the time the transaction was originally made. I can see this being both…