Fix for better performance on large tables

Calling .css and setting display none directly is apparently far faster,
so using it on tables with >1k rows should be better than show/hide.

This also contains https://github.com/tommyp/multifilter/pull/6 from
https://github.com/NanneHuiges

(I messed up the commit history and accidentally squshed it while trying
to fix some stuff)

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