Don't set any value for the table properties by default

When inserting a new table you get by default:

• width: 500
• cell spacing: 1
• cell padding: 1
• border size: 1

As a result the wiki syntax is bloated with in-line style what distracts the user from what is really important: the content.

(% style="width: 500px;" border="1" cellpadding="1" cellspacing="1" %)
|one|two
|three|four
|five|six

The default table styles should be set from the XWiki skin. Moreover, these in-line styles can break the PDF export.