Set type of PlotContext.children to List(Instance(Plot))
Simplify vm_props(), remove withvalues
Make finalize() return props to update that were finalized
Better error message from List.validate()
Remove 'recursive' option from Session.add()
Make Glyph deserializable again
Make DataRangeBoxSelectTool inherit from Tool
Merge branch 'cleanup' into bbexpose
Make tickers backbone objects that work correctly

Need to use initialize(attrs, objects) instead of the custom
constructors that they all had. Objects were not getting initialized
properly.  Alsofix up python side to pull grid tickers from an axis
object automatically.