Making CachingConfig.Policies lazy

Every time you access CachingConfig.Policies you call ConfigurationManager.GetSection() which isn't cheap. Let's read it once and wrap the call into Lazy<T>.
Update CachingConfigurationCollection.cs

When no element by specified name found, instead of trowing an exception, return the default.

Avoid NullReferenceException in Default.get
Merge branch 'patch-2'