Minor Send view improvements

[dstrukt]

As discussed in today's design call...

• The back button should be X, and should be pushed to the right corner
• The Scan button should be prominently displayed (as it more multi-purpose), and pushed to the top left corner / removed from next to the destination input

Additional considerations:

I have quite a few mocks that explore the different directions we can go with the Send flow, and discussed them in this most recent design call, but would love to pick over them again once we've cleaned up a few more pieces of the app.

e.g. do we have a keypad on the Send view, do we present the camera/scan functionality up front, and offer the manual entry as a secondary option on mobile, etc.. i still think we can dramatically improve the UX on this view (for mobile specifically)