64-bit integers are rounded before displaying

[adamhooper]

Steps to reproduce:

1. Add a Twitter Step
2. Duplicate the "id" column and convert it to text

Expected results: the Text "id" column and Number "id" column have the same values
Actual results: the Text "id" values are correct; the Number ones are incorrect

The problem: we send 64-bit integers as JSON, and the browser's parser converts them to Float and then converts them back to Integer to display them -- losing precision.

Solution: let's use a BigInt-compatible library for parsing JSON table data from the server.