api: Implement missing/empty fields for MVP

[mitjat]

Resolves #256

Implements all the fields that were added to the API in #247.

Most of the fields were straightforward, except for runtime balances. Changes introduced there:

• Spin-off PR Track native balances in runtimes. Per-denomination events from accounts module.  #288 to implement tracking of oasis-sdk balances in runtimes
• Moved /emerald/tokens to /emerald/evm_tokens; the former should be reserved for oasis-sdk tokens (currently only ROSE); internally renamed RuntimeToken->EvmToken
• Expanded /consensus/account to return the balances across all paratimes, simultaneously for oasis-sdk tokens and EVM tokens.

The last two points are not entirely coherent with each other: one splits the two kinds of tokens across two different URLs, while the other one unifies them. Both approaches have pluses and minuses; in the end, I decided for this combo because I think it best mirrors what the frontend needs, and we can always add endpoints that slice and dice and present (almost) the same information slightly differently.

I recommend reviewing commit by commit, as many of them are boilerplate.

[mitjat]

Thanks Andy!

[Andrew7234]

Looks good pending one comment.

Would appreciate if someone more familiar with the token logic could take a second pass through

[mitjat]

Thank again, Andy.
In the end, I added one more commit/change to the PR: I tweaked the presentation (= API output) of runtime tokens in that I split the formerly single list into two lists: oasis-sdk tokens and EVM tokens. The former merging always felt a little forced (as also alluded to in the PR description). Now I noticed that our UI mocks require yet another EVM-token specific field (name, which oasis-sdk tokens don't have) and that pushed me to fully separate the EvmBalance and SdkBalance types.