Controlling CAKE supply v1

By reducing the amount of CAKE made per block, we slow inflation. This has already been done once: Since the first reduction in block emissions, we've already effectively reduced the number of CAKE entering circulation from 40 CAKE per block to 14.5. But we don't want to do this too frequently, too early, for the same reason we don't want a hard cap: we still need to incentivize people to provide liquidity.