Large file imports fail due to db integer limit

[zstumgoren]

Files with byte counts too big for the standard Postgres integer field cannot be imported using the bulk load command (or, presumably, via the API).

The issue was recently encountered by another PANDA user, and I ran into it myself today.

I haven't yet verified, but the fix likely requires migrating the DataUpload.size field from a standard IntegerField to a BigIntField. This field is inherited from the parent abstract base class BaseUpload.

I'm working on a patch and will try to send a PR this week or next. Guessing this one might deserve another patch release, or perhaps it should be bundled with #941 into the 1.1.2 release?