Support Shapeshift.io authorization header

[eodgooch]

Shapeshift's API is introducing a breaking change. This means we need to update the shapeshift api module to include the new "authorization" header and a dynamic bearer token.

https://shapeshift.zendesk.com/hc/en-us/articles/360001186600-How-to-Authorize-Your-AUTHTOKEN-in-FireFox

[swansontec]

This work is underway. We introduced a new exchange API in #134, and we are in the process of splitting ShapeShift out into a standalone plugin to the core. At that point, you would be able to do something like edgeAccount.exchangeTools['shapeshift'].changeSettings({ bearerToken: '...' }).

[swansontec]

This is now supported in our application and in our API. The app asks for ShapeShift login credentials if that is the only available exchange that can do the trade. In our API, you would do account.swapConfig['shapeshift'].changeUserSettings({ accessToken: '...' }) to set this up.