Store submission times in UTC.
Store submission times in UTC.

Rationale:
1. Lexicographic sorting
2. Not leaking the system's time zone

btrask/stronglink,guiquanz/stronglink,guiquanz/stronglink,feld/stronglink,btrask/stronglink,Ryezhang/stronglink,iOSCowboy/stronglink,shaunstanislaus/stronglink,Ryezhang/stronglink,Lacra17/stronglink,yamingd/stronglink,shaunstanislaus/stronglink,shaunstanislaus/stronglink,iOSCowboy/stronglink,Lacra17/stronglink,nkatsaros/stronglink,btrask/stronglink,Lacra17/stronglink,nkatsaros/stronglink,feld/stronglink,rmoorman/stronglink,nkatsaros/stronglink,guiquanz/stronglink,rmoorman/stronglink,yamingd/stronglink,Ryezhang/stronglink,feld/stronglink,btrask/stronglink,yamingd/stronglink,rmoorman/stronglink,iOSCowboy/stronglink