Fix an image deletion issue where frame with svg:desc text is not properly deleted

problem: the text 'image description' is left bebind undeleted when trying to remove the image below
<draw:frame>
    <draw:image/>
    <svg:desc>image description</svg:desc>
 </draw:frame>

The fix is: apart from delete all the odf element from target node as we currently doing, we also want to delete all those text nodes that their parent are odf elements.

In addition, i also made small behavior change to getTextElements method of OdfUtils.
Now for character elements such as text:s, text:tab and text:line-break, it returns only the odf element instead of both element and text data.
Eg. if the given range include a <text:s> </test:s> element, it return only the <text:s> element rather than both <text:s> and ' '