Creating a generic file reader interface

This is a WIP still, but the idea is to add drag and drop support for GIS files onto the map.  I created a reader for a reduced geoJSON specification that is attached to the `glOsm` example as a proof of concept.  I haven't fully fleshed out the base `fileReader` class.

I think I will change the interface a bit so that rather than providing a single reader type to the map, there will be a function that will try to open the file with every available reader until one succeeds.  Then, there will be a map option to enable or disable drag and drop.
The idea is that you have a fileReader that adds features to a feature layer through the api.  The base class here provides a uniform interface to the HTML5 `File` and `FileReader` objects.  Here I have it storing the feature layer that it will draw on as well.