Introduce Spring Security ACL (Access Control Lists)

As described in #35, this PR introduces [Spring Security ACLs](http://docs.spring.io/spring-security/site/docs/4.0.x/reference/htmlsingle/#domain-acls).

The implementations are mainly based on [this tutorial](http://krams915.blogspot.de/2011/01/spring-security-3-full-acl-tutorial.html) (under impact of [this tutorial](http://www.denksoft.com/articles/acl-spring-security-tutorial/))

Here is a short list of features, that would be introduced by this PR:

  - Automatic creation of a H2-based ACL-database (separate from the SHOGun2 database)
  - (ACL-)Secured methods of the AbstractCrudService
  - Interception of the (secured) methods of the AbstractCrudService by using AOP/AspectJ in a custom AclManagement-aspect-class to create/update/delete entries in the ACL database. (This part has just been prepared and needs to be fully implemented.)
  - Full adaption of the webapp archetype to use/demonstrate the ACL mechanism.

Most parts of this PR are a **proof of concept**, which means that still some coding has to be done (especially to save/update/delete the ACL entries). But as it is working: **Try the webapp archetype and feel free to merge.**