Add entry point for napalm

[JoranHonig]

This will allow users to easily include slitherin detectors in their workflows:
#135

Example:

How to test

1. install napalm: pip install napalm-toolbox napalm-slither
2. run napalm collections list or the command as demonstrated in the picture above

Sidenote

I've not added napalm as a dependency.

If I understand pythons entry-points correctly then the napalm.py module would only be loaded by tools that actually load the entry point. Only napalm would do this, so there is no need to actually require it as a dependency.

This keeps things super clean for people that don't use napalm.

[olegggatttor]

@JoranHonig Could you please rebase these changes on develop? The flow is usually pr -> develop -> master. Thanks! Then, I will check the integration.

[olegggatttor]

Seems like we had sove divergence between develop and master. I pushed master to develop, could you please put now all your changes on top of the latest develop? Cause I see some strange files in your PR. Thanks!