Expose getTokens method from OrderbookYaml to the js SDK

[hardyjosh]

At the moment the js class for OrderbookYaml only has one getOrderbookByAddress method.

I want to be able to get all tokens. It should return:

• All under the token key
• All in a using-tokens-from json

These can be keyed like the gui.getAllTokens method on DotrainOrderGui (the logic should be centralised).

Unlike the gui.getAllTokens method which returns TokenInfo, we'll also need a way to know the network (as one OrderbookYaml can contain tokens for many networks). We could add chainId to TokenInfo.

[manny-uncharted]

I'd like to work on this issue

[manny-uncharted]

I've started out with understanding the repo and would like to give this a shot @hardyjosh

[hardyjosh]

You should also be able to get OrderbookYaml from the registry class