CLI: avoid importing anything until command is actually run

In prep for moving the server launch command into the main CLI path,
without imposing dependency on pynacl/etc.

src/wormhole/scripts/cmd_receive_file.py

@@ -1,13 +1,14 @@
 from __future__ import print_function
-import sys, os, json, binascii
-from wormhole.blocking.transcribe import Receiver, WrongPasswordError
-from wormhole.blocking.transit import TransitReceiver, TransitError
-from .progress import start_progress, update_progress, finish_progress
 
 APPID = "lothar.com/wormhole/file-xfer"
 
 def receive_file(args):
     # we're receiving
+    import sys, os, json, binascii
+    from wormhole.blocking.transcribe import Receiver, WrongPasswordError
+    from wormhole.blocking.transit import TransitReceiver, TransitError
+    from .progress import start_progress, update_progress, finish_progress
+
     transit_receiver = TransitReceiver(args.transit_helper)
 
     r = Receiver(APPID, args.relay_url)

src/wormhole/scripts/cmd_receive_text.py

@@ -1,11 +1,12 @@
 from __future__ import print_function
-import sys, json, binascii
-from wormhole.blocking.transcribe import Receiver, WrongPasswordError
 
 APPID = "lothar.com/wormhole/text-xfer"
 
 def receive_text(args):
     # we're receiving
+    import sys, json, binascii
+    from wormhole.blocking.transcribe import Receiver, WrongPasswordError
+
     r = Receiver(APPID, args.relay_url)
     code = args.code
     if not code:

src/wormhole/scripts/cmd_send_file.py

@@ -1,13 +1,14 @@
 from __future__ import print_function
-import os, sys, json, binascii
-from wormhole.blocking.transcribe import Initiator, WrongPasswordError
-from wormhole.blocking.transit import TransitSender
-from .progress import start_progress, update_progress, finish_progress
 
 APPID = "lothar.com/wormhole/file-xfer"
 
 def send_file(args):
     # we're sending
+    import os, sys, json, binascii
+    from wormhole.blocking.transcribe import Initiator, WrongPasswordError
+    from wormhole.blocking.transit import TransitSender
+    from .progress import start_progress, update_progress, finish_progress
+
     filename = args.filename
     assert os.path.isfile(filename)
     transit_sender = TransitSender(args.transit_helper)

src/wormhole/scripts/cmd_send_text.py

@@ -1,11 +1,12 @@
 from __future__ import print_function
-import sys, json, binascii
-from wormhole.blocking.transcribe import Initiator, WrongPasswordError
 
 APPID = "lothar.com/wormhole/text-xfer"
 
 def send_text(args):
     # we're sending
+    import sys, json, binascii
+    from wormhole.blocking.transcribe import Initiator, WrongPasswordError
+
     i = Initiator(APPID, args.relay_url)
     code = i.get_code(args.code_length)
     print("On the other computer, please run: wormhole receive-text")