* Calculate savings per swap relative to median values
* Update test mock quotes, add getMedian tests
* Identify assets by sourceToken and destinationToken
* Stop passing a gas param to the estimateGas call initiated in the swaps controller timedoutGasReturn
* Stop passing gas params to timedoutGasReturn
* Lint fix
* Stop passing no longer used param to setInitialGasEstimate
The `_fetchAndSetSwapsLiveness` was accidentally passed to
`setInterval` without being bound first, so the `this` reference was
not defined when it was called. It is now bound before being passed to
`setInterval`.
Erik Marks
Dan J Miller
Mark Stacey