Resolve core #1116 by removing fc::[io]fstream

[pmconrad]

Resolves issue https://github.com/bitshares/bitshares-core/issues/1116, also part of https://github.com/bitshares/bitshares-core/issues/1584 Requires https://github.com/bitshares/bitshares-core/pull/2047

This PR is a bit more dangerous than it seems. There are subtle differences in fc's stream implementations, in particular wrt error handling. fc is non-standard and even inconsistent in that regard, which is one more reason to get rid of it IMO.