CouchClient Convenience Constructor

Added a convenience constructor to CouchClient so a  conventional connection 
string can be stored in the App.Config or Web.Config and the name can be 
supplied to the contstructor.

A new class called ConnectionSettings parses the connection string and places
each piece in static members so they can be used to construct the CouchClient.

The Database name can be accessed later whenever a CouchDatabase instance is
needed.

Included a test for the new constructor in CouchClientTests.