Addition of Drag Selection + Better Customization of Resize handles

Hey,

I added to Scene the ability to do drag selections (if enabled).  This meant that that I had to create a new method called pickNodes which select a set of nodes within a region that match the passed conditional.

I also updated the resize handles to be able to have different stroke/fill colors.

Also I added a small performance optimization to the Text to prevent measuring on construction so that developers can finely control when measuring takes place since it is so slow

Billy