Add KeyStore Implementation of KeyProvider

The purpose of this issue is to create a new implementation of the KeyProvider interface supported by an instance of java.security.KeyStore.  This implementation should support configurable KeyStore Location, Type, and Password properties in order for the implementation to work with the types listed in the NiFi KeystoreType enumeration.  The implementation should be capable of reading SecretKey entries from the configured java.security.KeyStore and making them available to calling components.  The approach should provide a more standardized format for accessing SecretKey material to support encrypted repository implementations.