Use Dynamic Fee for More than Just attach (?)

[adamkrellenstein]

When Counterparty was first created, the XCP fees for various transactions were hard-coded to low, constant values (e.g. 0.5 XCP for issuing a named asset). This system was chosen for its simplicity, but it creates significant friction when onboarding users to the Counterparty ecosystem (esp. since it is so hard to acquire XCP) and yet the fees are so low that they have little economic significance for market participants. It doesn't create meaningful demand for XCP; it's just a PITA.

A proper XCP fee system should be proportional to network traffic and transaction complexity while reducing unnecessary barriers to entry into the network. When transaction volumes are low, the fee should be exactly zero; when they're high, they should go up quickly. This should simultaneously reduce the barriers to entry into Counterparty and increase long-term demand for XCP.

We've already implemented such a system for attach transactions—it's described here: https://docs.counterparty.io/docs/advanced/specifications/gas-system/ This issue is a proposal to use the above gas system not just for attach transactions but also for named asset issuances, etc.