Metadata pane should be refreshed on a notify() event for the selected item

[dstillman]

Currently the metadata pane doesn't update after a notify() until you click away and back.

It's unclear what should happen if the user is in the middle of editing a field when a notify() for that item comes in, but considering fields are saved on blur(), there's not much that should cause a notify() while a text field has focus...

#67 is dependent on this bug, since undo will often be called on the currently selected item.