Integrate proper CP calculation

[rossneilson]

Currently there is a basic clearing price calculation in the useBids hook for the fairsale page. However the solution taken from gnosis for this calculation in src/aqua/Price.ts should be more like what we really want. Some of the variables and data used in the function seem strange and Im not sure entirely what they are supposed to be from. Time will be needed to understand this, likely with reference to the final clearing price in the SC to adapt it to work in the UI properly.