add ophydregistry to instrument package startup

[prjemian]

__all__.append("registry")
from ophydregistry import Registry

# after defining the default timeout for EpicsSignalBase

# Create a registry of ophyd devices
registry = Registry(auto_register=True)

where

auto_register
  If true, new ophyd objects will be registered without needing to
  call ``register()``.

@canismarko: This will be easy.

[prjemian]

Closed as part of #245