Fix the response code for user credentials grant type

Fixes Issue #290
Fix credentials grant type test to assert that the response code for an invalid username and/or password is 401
fixes lack of namespaces in comments
adds Cassandra storage
Merge pull request #311 from bshaffer/add-cassandra-storage

adds Cassandra storage
Merge pull request #298 from adambutler/patch-1

Fix the response code for user credentials grant type
more information on skipped storage when applicable
Merge pull request #313 from bshaffer/more-information-on-skipped-storages

more information on skipped storage when applicable
Initial commit.
Move crypto token storage initializing to the server constructor.
Refactor getAccessTokenResponseType().
Add store_encrypted_token_string to the default config array.
Add createDefaultCryptoTokenStorage().
makes suggested improvements on @bojanz PR and adds tests
ensures that access_token storage is CryptoToken, even if defaults are set otherwise, using CryptoTokenInterface
Merge pull request #318 from bshaffer/bojanz-improve-crypto-token-dx

Bojanz improve crypto token dx