[enhancement] Add "Max" or "All" to swap page

[laboon]

A useful feature is the ability to automatically swap all of a given token for another ( https://kintnet.interlay.io/swap ). I recommend adding a "Max" button which will set the amount to swap to the entire amount of that token that the user has. For an example, see HydraDX's page ( https://app.hydradx.io/#/trade ).

[danielsimao]

@laboon Thank you for raising this issue.