Unmanaged / annonymous cache

[cruftex]

At the moment every cache needs a unique name.

This is needed to have an unique identifier for JMX. We will need it later for external cache configuration, too.

The unique name requirement leads into trouble, when the cache instance has only a temporary or limited lifetime. Applications need to take care that a cache is properly destroyed since it is not garbage collected.

TODO:

• Support for a cache that needs no name
• Cache should be GCd when originator has no more reference on it
• We should keep a WeakReference / make statistics available what caches exist
• on finalize we need to do a proper destroy and make sure the cache has no
  thread/timers.

[cruftex]

Dropping this for v1, since we have no real use for it at the moment.

[cruftex]

Current status:
If no name is specified a unique name is generated. This means caches can be created dynamically without the need of giving them a name.

I see that EHCache 3 has a UserManagedCache which is not associated to a cache manager. However, the created cache must be closed explicitly again to free resources. That makes it basically not different from the capabilities we have already.

Removing the milestone, since we don't need that at the moment. If somebody else has reasons please comment.

[cruftex]

Properly clean timer tasks that hold a reference to the cache.
See: #167

[cruftex]

Decided to drop this issue, since things would get very ugly and the benefit is questionable.
W.r.t. lifetime control the Cache class/interface should not have different behavior depending on the configuration. If there is a strong case for this, we can reevaluate.