Ignore default namespace declarations

I've added a function that can ignore default namespace declarations in the first element within the body element (issue #470) ```xmlns:tns="SAMPLE"```. And removed unnecessary ```tns:``` declarations in all elements when not needed.

Also build a test which checks the functionality.
Would be awesome if you could write the comment in a JSDoc style, like:

```javascript
/**
* Returns true if a schema namespace needs to be ignored.
* 
* @method shouldIgnoreNamespace
* @param {Object} schema   The parsed WSDL Schema object.
*/
```