Filter extraneous denominations from runtime transaction amounts

[pro-wh]

The Explorer team merged a PR to filter out extraneous denominations: oasisprotocol/explorer#1546

We can also do this in Nexus by checking the Amount denomination against the known denominations for each runtime according to the oasis-sdk.

[Andy] I'm a bit reluctant to start this since opinionated filtering/data manipulation was intentionally not in scope for Nexus. Nexus is intended to make on-chain data queryable, and downstream applications can filter/sort the data as needed. If possible we'd like this change to be made upstream in oasis-core, but already talked with them and it looks like sending 0 amounts of arbitrary tokens is allowed under evm standards and so the change won't be made upstream.