Added viewer url query parameters

Added support for the following viewer url query parameters: center,
level, token, url (for a map service).  Still testing.  Support for the
"url" parameter is not as complete as in the ArcGIS.com viewer.
Currently, this parameter can specify a map service or a dynamic
(filtered) map service, but not a feature service or a map service
layer.
Removed displayslider code snippet

Removed code snippet also removed from Esri master branch.