Zoom defaults to edge of reference layer in map input for application

[phendricks]

Currently, the map input for an application defaults either to a global view of the United States or to a fixed boundary. Usng a chained application, it would be an extremely useful option to be able to specifiy spatial objects (points, lines, polygons) in the first application and then allow the second application to zoom in appropriately to those spatial objects. This could be done by either specifying a custom zoom level and using those spatial objects as a center through a reference layer, or by allowing the zoom's boundary to contain all the spatial objects (similar to the map reporting tools).