P2P swaps of project tokens

Background

Currently, there is not way for holders to trustlessly do p2p (e.g. OTC) trades for $CRT, this would be a nice feature. This means such trades would now have to involve some sort of custodian - which may or may not exist, or engage in risky transactions where there is a risk of defection.

Question

The ability of a holder to offer $CRT in exchange for specified amount of $JOY to a specific beneficiary member, where this member will need to accept and pay to execute the swap. The $CRT have to be liquid at the time of initiation. It should, like normal transfers, also be possible for the channel owner to initiate such swaps with an accompanying vesting schedule aligned with the time of acceptance, just like they can for normal transfers. The initiator can always cancel the pending swap at any time while it has not yet accepted. $CRT which is encumbered by a such a pending swap cannot be used for any other activity, like staking for revenue splits, transfers, issuer sale, AMM, etc., they should not count as liquid any longer

The main challenge here will be to add a new way of locking $CRT for this purpose which dose not complicate accounts much further. We have a recurring need to add new ways of locking funds, beyond staking. This can get messy.

Start by reviewing the existing account locking, staking, transfer, and vesting flows in the Joystream repository to understand how funds are currently encumbered. Define how a pending $CRT-for-$JOY swap is created, accepted, cancelled, vested, and excluded from other activities; done means the design resolves these lifecycle and locking interactions without complicating accounts.