Added a new module: shogun2-security.

The new (maven) module provides a basic AuthenticationProvider and should be used for the further implementation of security-related stuff.
The new shogun2-security module is required as a dependency of the shogun2-service module.
Webapp-Archetype is using the new security module.
Merge pull request #2 from buehner/spring-security

Added a new (security) module.