This also moves DebugLinkMixin to debuglink.py and converts the mixin to
a subclass of TrezorClient (which is finally becoming a
reasonable-looking class). This takes advantage of the new UI protocol
and is ready for further improvements, namely, queuing input for tests
that require swipes.
The ui.py module contains a Click-based implementation of the UI
protocol. Use of callback_* methods has been limited and will probably
be cleaned up further (The contract has changed so we'll try to make
third party code fail noisily. It is unclear whether a backwards
compatible approach will be possible).
Furthermore, device.recovery() now takes a callback as an argument. This
way we can get rid of WordRequest callbacks, which are only used in the
recovery flow.
