Reserve Withdrawals

[migueldingli1997]

New messages:

• MsgWithdrawReserve: withdraws tokens from the reserve (available both from CLI and REST). Only allowed if the withdrawer is the bond's controller DID, and if the bond is in the OPEN state and has enough available reserve.

New fields in bond type:

• ReserveWithdrawalAddress: destination address of any reserve tokens withdrawn via the MsgWithdrawReserve message. This is specified during bond creation and is not optional.
• AvailableReserve: coins value specifying the remaining reserve out of the current (virtual) reserve. This will only ever not match with the current reserve if the MsgWithdrawReserve message is used. This defaults to nil (empty coins) and is not specified during bond creation.
• AllowReserveWithdrawals: bool specifying whether reserve withdrawals by the controller DID are allowed. This is specified during bond creation and is not optional (however if excluded from the CLI, it is assumed to be False).

New queries:

• QueryAvailableReserve: gets the bond's available reserve (available both from CLI and REST)

New invariants:

• AvailableReserveInvariant: ensures that the sum of all the 'available reserve' values being reported by the bonds matches the balance in the global reserve pool.

Other changes:

• Updated documentation and scripts/demos
• Renamed WithdrawReserve function to WithdrawFromReserve to avoid clash with new message
• Renamed DepositReserve function to DepositIntoReserve to match above change

Interesting points:

• Wherever we use setReserveBalances, we now also update the available reserve via setAvailableReserve
• Sells are not allowed when reserve withdrawals are enabled (so the two bools cannot be True in the bond)

[dferendo]

Looks good to me