ItemCollection - restrict to basic types

[rsoika]

A ItemCollection should not store values which are not in the group ob basic types:

// test raw array types first
	if (o instanceof byte[] || o instanceof boolean[] || o instanceof short[] || o instanceof char[]
			|| o instanceof int[] || o instanceof long[] || o instanceof float[] || o instanceof double[]
		    || o instanceof XMLItem[]		
			) {
		continue;
	}
		// test package name
	Class c = o.getClass();
	String name = c.getName();
	if (!name.startsWith("java.lang.") && !name.startsWith("java.math.") && !"java.util.Date".equals(name)
			&& !"org.imixs.workflow.xml.XMLItem".equals(name)) {
		return false;
	}

This restriction is currently implemented by the XMLItem class.
But we should also avoid this basically on the ItemCollection level itself.