3 Data related changes

Three things are going on here:
1. we're tweaking the css for the data pane to keep the panes scrolling (it's stupid)
2. we're adding a `patchModelAttributesChange` method for observing attribute changes
3. we add the idea of a `modelGraveyard` where models go when they're destroyed. Importantly models are removed from the data pane when they're no longer active.