Fix parsing table cells

[plutasnyy]

This PR:

• Fixes removing HTML tags that exist in cells
• stripping function was in general problematic to implement in easy and straightforward way (you can't modify descendants in-place). So I decided instead of patching something in table cell I added stripping everywhere in the same consistent way. This is why some tests needed small edits with removing one white-space in each tag. I believe this won't cause any problems for downstream tasks.

Tested HTML:

<table class="Table">
    <tbody>
        <tr>
            <td colspan="2">
                Some text                                        
            </td>
            <td>
                <input checked="" class="Checkbox" type="checkbox"/>
            </td>
        </tr>
    </tbody>
</table>

Before & After

'<table class="Table" id="..."> <tbody> <tr> <td colspan="2">Some text</td><td></td></tr></tbody></table>'
'<table class="Table" id="..."><tbody><tr><td colspan="2">Some text</td><td><input checked="" type="checkbox"/></td></tr></tbody></table>''