Fixed bug in Azure output cache provider with tenant names containing non-alphanumeric characters.
Removed all Azure-related assembly references from Orchard.Web.csproj.
ICacheProvider calls Start() and provides the region prefix as a
property, which lets us create a dedicated DataCache.
The BuildCache method is called once per record, and reuse by
Nhibernate.
There is no way to configure the cache provider for specific tenants,
thus ignoring it. NHibernate should take an instance instead of a type
for the provider.
Added clear exceptions in provider constructors when settings are missing or invalid.
Refactored cache client configuration and creation into separate class.
