Moved layer list to separate module.
Fixed apply button in sublayer list to work in Firefox.
Layer list configuration now loaded from JSON file.
Added README.md
Modified web.config to remove .json handler before adding it.
When a layer cannot be loaded it's checkbox is disabeld and styled.

Also added a test to see if the browser supports HTMLElement.dataset
property.
Now explicitly set map scale levels in map constructor.

Fixed bug in layer list: removing progress node from incorrect parent.
Added support for `config` query string parameter.
Merge pull request #2 from WSDOT-GIS/config

Added support for config parameter