issue#1009

form -> from

[WebUI] Hide public address if not available

setuptools doesn't like it.

- hddtemp is not installable using pip, remove it.
- conditionalize scandir dependency
- add py3sensors

Note: pip >= 6.0 is required.

- scandir package is only needed for Python < 3.5.
- the name of extras are now lower case (easier to type/read).

Note: setuptools >= 18.0 is required.

Just to be clear.

Some cleaning while I'm here.

That's way better than checking for the OS; psutil may implement it for
new platforms in the future.