Deposit / withdrawal issues

[andywer]

A critical issue was brought to our attention:
If you try to deposit or withdraw with anchorusd.com (and potentially other anchors, too), you get stuck on the second transfer view where it shows the fee, since the button to proceed will always be disabled.

Then we stumbled upon another, smaller issue: The default value of the deposit/withdrawal asset selector tends to be an asset that the user doesn't have a trustline for.