Let RandomAccessibleInterval extend IterableInterval with default implementation

There is really no reason that RandomAccessibleInterval should not be Iterable. We already can make any RAI iterable using Views.iterable(). With default implementations of IterableInterval in RandomAccessibleInterval, there is no overhead for implementers of RandomAccessibleInterval (unless they want to support more efficient, specialized cursors).

Consequences:

Views.iterable() is @Deprecated because one can call cursor() on RAI directly.
Views.flatIterable() now returns RandomAccessibleInterval "officially".

I fixed one new bug that was introduced by this:

void doSomething(IterableInterval<T> ii)
{
    ...
}

void doSomething(RandomAccessibleInterval<T> rai)
{
    doSomething(Views.flatIterable(ii)); // This becomes a circular recursion now
}

Probably there will be a few more bugs of this form. But I think the added convenience of returning RAI from Views.flatIterable() is worth it.

imglib / imglib2

Let RandomAccessibleInterval extend IterableInterval with default implementation #361