Capabilities definitions should be presented more clearly

[travis]

As Alan pointed out, our current pattern of copy-pasting the JavaScript capability definitions leaves a lot to be desired - dependencies aren't fully expressed, the definition language is not especially intuitive for non-JavaScript programmers, etc.

Let's figure out a nice, relatively language-neutral way to express capability definitions!

[vasco-santos]

In w3-filecoin spec we are using a neutral language https://github.com/web3-storage/specs/blob/main/w3-filecoin.md#filecoinqueue

Not sure if it is the best way, but we also have been talking about updating to the new UCAN spec namings once we can do an entire refactor of this (and upgrade them in ucanto)