Improve QR Move SCP

[scaramallion]

The interface for the QR Move SCP could use some work:

• ~The code itself is fairly spaghettied (as is Get) which makes changes harder than they should be~
• ~No simple way to set the configuration of the association with the move destination (particularly the presentation contexts)~
• All the transfers happen over the same association which means hitting the limitations of the DICOM presentation contexts negotiation system
  • This last one depends on the user, but maybe we can track the number of contexts that have been used and if > 128 restart the Storage SCU connection?
  • Alternatively provide a method for the user to restart the Storage SCU connection

[scaramallion]

Possibilities...

1. When yielding the (address, port) of the Move Destination allow the user to optionally yield kwargs to pass AE.associate(). This seems like the simplest option to control the presentation contexts and is relatively simple to implement so it could be done in v1.5
2. Add a new event evt.EVT_C_MOVE_ASSOC, although I don't think it'll be flexible enough

The form:

try:
     something()
except Exception as exc:
    logger.error('some failure str')
    logger.exception(exc)
    rsp.Status = 0xC514
    self.dimse.send_msg(rsp, context.context_id)
    return

is also used a lot, maybe we can replace it with a context instead?

with attempt(msg='some failure str', status=0xC514):
    something()