[BUG] Make library not single threaded and more DI-able

[eByte23]

Essentially this is currently single threaded and really can't use di because of all the inline ctor deps

Actions:

• Find all constructors where classes inherit interfaces that are created dynamically make the initialised with method on interface not ctor.

• Change where all documents are signed to a signing provider so it all uses the configuration of what hash type etc..

• Classes like Saml20Metadata, Saml20AuthNRequest, etc.. remove the constructors as this is a stupid way of doing shit and its all over the shop