Prop 158: Adding special asset pairs for stDYDX -> DYDX

Adding special asset pairs for stDYDX -> DYDX. Please vote 'Yes' if you support to this proposal, and 'No' if you oppose it. Commonwealth post for stDYDX -> DYDX : https://commonwealth.im/ux/discussion/15494-asset-listing-stdydx-proposed-parameters.