Added support for a partition key prefix based on a configuration file
value. If a value shall be loaded based on a configuration setting a
PartitionKeyPrefixKey can be used to load the value from the cloud
configuration file or the app/web.config appSettings.

+Some minor comment spelling edits.
Refactored out all storage account and config access to a new class called ConfigManager
Merge pull request #11 from wendelstam/master

Support for a optional PartitionKey prefix