Ability to update fulfillment

[lightclient]

If basically everything about the bounty is available to be updated, I think it makes sense to also allow fulfillers to update their submissions. Once a submission is accepted, it should lock any new changes.

[lightclient]

It may also make sense (for all place where changes are possible) to think about how users will be informed of changes and how we will store that information.

[PhantomCracker]

Any news on the actual bounties? How do they work? How can we work on it? How are we paid?