[Slug] Implemented TreeSlugHandler prefix/suffix

This PR should address the requirements described in #891.

At the moment I am still trying to fix the basic prefix (test was added). Instead of ```test.foo/test.bar/test.baz``` it results in ```test.test.test.foo/bar/baz```. But when I handle the prefix earlier, it results in ```test-foo/test-bar/test-baz``` (it transliterates the dot). This is not correct, because the prefix/suffix should not be transliterated.

Need some help over here, someone?