Introduce "pro" account tier

[Klakurka]

This would be a simple setting on each account.

Pro accounts would have the following benefits:

• higher "payment trigger" throughput (either a higher rate limit or support for triggering on micropayments.
• multiple payment triggers with overlapping addresses

[Klakurka]

Scope / issues left:

• We'd need to add the limiter on this.
• Send user a free-of-charge email notification when any of their limits (currently only email and post msgs) are nearly reached (say, 10 away).
• Add info warning in site header area if they're about to hit their limits.
• Change limits to be monthly.
• New users not getting the full 100 emailCredits on account creation. Right now they only get 5 for some reason (at least in prod). So because of this, new players see this without having setup any receiving emails:
• New users not getting the full 100 postCredits on account creation. Right now they only get 5 for some reason (at least in prod).