trezor: split pinentry tool into a separate file

libagent/device/ui/__init__.py

@@ -0,0 +1 @@
+"""UIs for PIN/passphrase entry."""

libagent/device/ui/simple.py

@@ -0,0 +1,6 @@
+"""Simple, cross-platform UI for entering a PIN/passhprase."""
+import sys
+
+import pymsgbox
+
+sys.stdout.write(pymsgbox.password(sys.stdin.read()))