Enforce more secure XML encryption

[cjbarth]

Add newer encryption algorithms and remove insecure ones.

Checklist:

• Issue Addressed: [ Addresses better integration with xml-encryption 1.1.0 release #429 ]
• Link to SAML spec: [ n/a ]
• Tests included? [ yes ]
• Documentation updated? [ n/a ]

[markstos]

Here's a reference to Triple DES being considered insecure now:
https://security.stackexchange.com/questions/146710/is-the-3des-algorithm-secure

Here's a reference about AES 256 GCM being considered secure:
https://security.stackexchange.com/questions/184305/why-would-i-ever-use-aes-256-cbc-if-aes-256-gcm-is-more-secure

And regarding the final addition, AES-128-GCM, this reference says it's preferable in some cases over AES-256-GCM for performance reasons:

https://crypto.stackexchange.com/questions/77750/why-gcm-operation-mode-with-aes-128-is-recomended-and-can-we-use-aes-192-and-aes

Given the above, I approve this for 3.0.0, which is making other breaking changes anyway.