python3: sync build rules with python's

Signed-off-by: Alexandru Ardelean <ardeleanalex@gmail.com>
open-plc-utils: import from oldpackages

Signed-off-by: Florian Fainelli <florian@openwrt.org>
Merge pull request #572 from commodo/python3-sync-build

python3: sync build rules with python's
open-plc-utils: add license information

Add licensing information for the open-plc-utils package and update the
copyright.

Signed-off-by: Florian Fainelli <florian@openwrt.org>