Fixes #77

For details see:
http://www.quora.com/Django-web-framework/When-using-Djangos-signals-where-should-the-code-that-registers-a-new-receiver-function-go
Merge pull request #79 from Walkman/fix_delete

Fixes #77
remove redundant re-raising of swallowed exception
Merge pull request #80 from MontmereLimited/exception-swallow

remove redundant re-raising of swallowed exception
moved signals to listeners.py, imported from models. fixes #81
move version directly into setup.py

because if you are doing stuff in __init__.py, setup.py will try to load
it on install, which can cause some problems when resources aren't
available on an initial install
Merge pull request #82 from MontmereLimited/master

move version directly into setup.py
Merge branch 'master' into shared-models-v1