[Extended Protocol] S->C Mix Success Rate

[nitoygo]

Is your feature request related to a problem? Please describe.
In relation to #576, can we extend the protocol such that the server sends the actual % as computed in the server side to the client?

Describe the solution you'd like
Instead of the client having to compute (or maintain its own formulas), let's have the server detect the state of the mix inventory, if it's mixable, check the percentage and send it to the client.

Additionally, we can include the cost (in zen) in the packet