example: split library and example

[aeneasr]

As @danilobuerger suggested, it is smart to split the example and the library repository. I've set up a repository at https://github.com/ory-am/fosite-example

In the process, we need to keep the storage mock in the core library as some tests depend on it.

Another feedback by @danilobuerger was that server and client should be separated in the fosite-examples. I agree.