Use table.iter api with readable stream for loading large data files

[RandomFractals]

see changes in #49 and table schema docs: https://github.com/frictionlessdata/tableschema-js#tableiterkeyed-extended-cast-forcecast-relations-stream--asynciterator--stream

[RandomFractals]

Tried it with vizgen mouse genome data: https://vizgen.com/data-release-program/

One of their data files is ~207 Mbytes, has 650 columns and over 78K rows. That's about 50 million of dense wide column mostly numeric data points to parse.

This took a while to load and Tabulator table is not very responsive on scrolling ...

I might need to move reading large data files to a worker thread because of all the CSV line data parsing. Docs on nodejs worker threads: https://nodejs.org/api/worker_threads.html

Even with the added table.iter rows stream reader, ext. host main thread is blocked till all data is read and the first 1K rows are sent to the table webview for display.

[RandomFractals]

Closing this. Will handle the rest of large CSV data parsing and loading optimizations in #58 and #59.