Add withLocalTx getting a supplyer task and returning the result

[JanWiemer]

As far as I understand it, there are two general ways for running transactions:

// Option 1
...
JacisLocalTransaction tx = container.beginLocalTransaction();
// Do work
tx.commit();

...

// Option 2
container.withLocalTx(() -> {...});

If I'm not mistaken, using option 1 would not result in a rollback being executed if an exception occurs in my block of work, while a rollback would be attempted when using option 2 and exception occurs.
Assuming this is the case, wouldn't it make sense to offer something like public <T> T withLocalTx(Supplier<T> task) alongside the existing public void withLocalTx(Runnable task)? I often find myself in lengthy transactions that in the end produce some value which I want to return.
Not sure if the above is a feature request or if I'm just missing something...

Originally posted by @fullben in #19

[JanWiemer]

will be includes in version 2.0.7