Exponential Price Decay Contract merged

I have just now merged the new Exponential Price Decay Contract into master.

In response to the community review, we have reduced the time of the decay from 28 days to 21 days by subtracting the price at 21 days from the curve. The contract now does not hardcode this, but takes the startPremium and totalDays as arguments to the constructor which controls the starting price and the days it will run for.

I would invite anyone from the community to review the contract and if there isn’t any issues we’d like to to put the contract to a proposal. Concurrently frontend should be ready to be deploy with the contract in the next week or so.