@Persistable annotation support which enables using a writable session during the annotated method call

My short-term goal is to avoid #refresh() invocation on the default
session by using only writable session in the annotated operation (@Persistable).

If an operation of JAX-RS Service is annotated by @Persistable, then HstRequestContext#getSession() will return a writable session by default.
This lets us use writable session only during the method invocation.

Of course we still have to re-fetch beans, but my idea can improve a
little by avoiding another #refresh() call. See the examples below.

Regarding "how can you know what other code was already executed and
fetched virtual nodes?":

• This is not my short-term improvement goal yet. So, the
  architectural enhancements could save this situation in the end.
• My solution is about the short-term improvement only.

Let me explain my small improvement again here with examples.

Currently, I have to write this, for instance:

public void updateDocument(...) {
scopeBean = getMountContentBaseBean();
document = findDocument(scopeBean);
wpm.update(document);
requestContext.getSession().refresh(false); // This is needed
// because document is from default session
// while wpm is from writable session
scopeBean = getMountContentBaseBean();
document = findDocument(scopeBean);
}

I'd like to write like the following instead:

@Persistable
public void updateDocument(...) {
scopeBean = getMountContentBaseBean();
document = findDocument(scopeBean);
wpm.update(document);
document = findDocument(scopeBean);
}

If the document is retrieved from #getContentBean(), then the examples
will get shorter.

My small improvement idea is just about removing another #refresh() call
as you may see. And, scopeBean doesn't need to be re-fetched.

My idea is just about a small improvement in the short term, looking
less important.
But, I think this can improve the following:

• Removes error-prone steps with #refresh(), which is caused by using
  two different jcr sessions. One session for fetching/updating with
  annotation.
• Code readability. Much simpler.