Reduce accumulation requirement for zerocoin minting; educate users on use and risks.

At this time, zerocoins are not widely used, and even less understood. As such, we end up advising people on how to disable the automatic minting of zerocoins. This, inevitably, deters new users as they don't necessary know to disable it at the beginning, and therefore it is not a pleasant experience at the outset.

Instead, have the autominting off by default, however not disabled so that those that understand it can utilize it. This needs to be followed by better education of the coin users, so that they can decide if they wish to enable it, or leave it off.