KeepKey / Trezor: client split

We're going to want to do a few things differently, such as
device recovery.  So move the client code to clientbase.py
and create a per-plugin client.py file for the derived client
class.

plugins/keepkey/client.py

@@ -0,0 +1,14 @@
+from keepkeylib.client import proto, BaseClient, ProtocolMixin
+from ..trezor.clientbase import TrezorClientBase
+
+class KeepKeyClient(TrezorClientBase, ProtocolMixin, BaseClient):
+    def __init__(self, transport, handler, plugin, hid_id):
+        TrezorClientBase.__init__(self, handler, plugin, hid_id, proto)
+        BaseClient.__init__(self, transport)
+        ProtocolMixin.__init__(self, transport)
+
+    def recovery_device(self, *args):
+        ProtocolMixin.recovery_device(self, True, *args)
+
+
+TrezorClientBase.wrap_methods(KeepKeyClient)