toward rendering table using polymer templates

NOTE: not final. Sort is not working.

Benefits:
More readable
More polymer style
With data binding, renderGrid doesn't need to be called to update table.

Issues:
Sort stopped working (obviously because it is not bound)

General issue: There is something static in the implementation. If you put two instances of of csv-preview in a page, updating one's data changes the other one as well (I will open a separate issue for that)