Make all storage use fsync
Make all storage use fsync

Hopefully costs little and increases robustness.
Closes #75

Crowndev/electrumx,Crowndev/electrumx,thelazier/electrumx,Groestlcoin/electrumx-grs,bauerj/electrumx,bauerj/electrumx,shsmith/electrumx,erasmospunk/electrumx,thelazier/electrumx,erasmospunk/electrumx,Groestlcoin/electrumx-grs,shsmith/electrumx