Currently, local module discovery is broken with luigi installed from
this derivation.
In the documentation, you can see the following command line syntax
used:
```
luigi --module module_name ...
```
However, currently this will result in an error:
```
ModuleNotFoundError: No module named 'module_name'
```
However, if the call is prepended with this:
```
PYTHONPATH=.:$PYTHONPATH
```
then it will work as expected.
This patch makes this the default behaviour.
This commit renames the pythondaemon module to match its module name, github
name, and pypi name, which makes it easier to find and reference. In order to
avoid breaking any external users, I've left an alias with a deprecated warning.
