[WIP] Add messy import

This is very WIP. Fyi @domoritz 

I was initially thinking that we should use messytables to figure out the schema (types & column names), delimiter, quote, end-of-line chars, etc. of a CSV-like file, then use that to construct an `FileScanEncoding` for use in ingest.

I now wonder if we shouldn't instead use messytables to parse the file and then use the row iterator to upload. This would be equivalent to, say, generating a CSV on the fly and pushing those bytes instead. Perhaps this would use Andrew's streaming `PUT` method for writing data to a table.

Thoughts?