[research] make applications private from hub by using ETH/asset for the metachannel instead of the application itself

[emansipater]

Right now, for simplicity, the playground opens applications directly as metachannels across the hub. This means that the hub sees and technically can derive the identities of which applications are open (though not individual updates to that application).

For optimal privacy, what should actually be done is that an asset path for the underlying collateral (such as ETH) should be opened instead, and then the application opened against that asset metachannel. This way the hub does not know which applications are being used, only which net asset flows result once all applications using the assets are closed out and the asset metachannel is terminated (this also can be improved in the future, but that is a much more complicated task).

[snario]

@IIIIllllIIIIllllIIIIllllIIIIllllIIIIll Can you dump the notes you have on this so far? I feel like we already know enough to just implement this but it would be useful to write it out here, first.