Allow to drag rows even when user click to not "TD" node

[kkozlik]

fix #93

[brendon]

THanks @kkozlik, @isocra, can you remember why you're only allowing the TD to be dragged?

[isocra]

Hi @brendon, I can't remember off the top of my head why it's the case. I remember that it was quite tricky to cells that have complex html in them (e.g. nested tables). Do all the example tables still work with this change?

[brendon]

Thanks @isocra, looking at https://github.com/SortableJS/Sortable they disable text selection (aka allow the whole row to be dragged) unless a handle is defined. I guess @kkozlik, if you can check that nested tables etc... work with this change, and that the .handle functionality still works (and allows text selection and link clicking etc... on the non-handles then I guess this one is ok to merge :)