Speedup while finding 'td' elements in the first row

We don't need to find all td's with `$('td')` and then look if they are in the first row.
Finding all `'td'` suffices I think. Large tables can throw a stack-size error otherwise:

    Uncaught RangeError: Maximum call stack size exceeded
Merge pull request #5 from NanneHuiges/td_search_speedup

Speedup while finding 'td' elements in the first row