Adding first validators for response processing

- Added Response Processor
- Added Various Validators
- Throwing detectable exceptions for backwards compatibility
Extracted lambda to private method, added test
Add test for the response destination match validator
Minor docblock tweaks
Adding tests for the validation result
Expanded configuration with additional requirements
Updated keyload to make use of interface
Expanded the decryption provider configuration interface

added the required private key, as well as optional private keys
updated the simplesamlconverter acccordingly
Extracted file loading to a utility.
Added the ability to load private keys for decryption
Added ability to decrypt encrypted SAML2 Assertions
Add the ability to check whether or not attributes are base64encoded
Adding Assertion processing, the decryption, validation and processing
Implemented the SubjectConfirmation NotOnOrAfter check
Implemented SubjectConfirmation Recipient match check

Also refactored the destination checks to use a value object
Adding Assertion Processing to the Response Processor
Implemtened SubjectConfirmation InResponseTo validation
Refactored Response Processor API for easier integration
Expanded Collection Functionality
Added tests for the destination value object