Warning when close step modals

[Agupane]

Once you start an operation (lock/unlock tokens, orders, etc) and if you close the modal before the transaction finished, once the operation finished, it will throw a warning on the console.

It's better to test it on kovan, because the time between the operation starts and finish it's good enough to let you close the modal

[unjapones]

I'll wait for #216 to be completed before taking a look at this because it may make things easier to fix (if this still present at all after that).