Improve flexibility of ImageNamespace.normalize methods

By means of the `ImageNamespace` it is currently not possible to do the following:

```java
Img in = generateByteArrayTestImg(true, 5, 5);
Img out = ops.create().img(in, new DoubleType());
ops.image().normalize(out, in);
```

The reason is that the method declaration says:

```java
public > IterableInterval normalize(
final IterableInterval out, final IterableInterval in)
```

That is, the types of elements output and input have to be same.

Start by inspecting the ImageNamespace.normalize method declarations and the shown call pattern using ByteType input and DoubleType output. Determine how the generic types constrain input and output, then verify that normalization supports differing element types without breaking existing behavior. Done means the example call is valid and the existing normalize behavior remains covered.

Written by the indexing model from the issue text.