Implement NetworkManager or NMCLI backend to RaspAP

[navado]

Instead of reinventing NetworkManager use it as backend for all network and wifi related operations. nmcli is command line utility to manage most of the aspects of the networking in Linux. NetworkManager is de-facto standard software to configure network in Linux based distros.

[bz edit: typo]

[navado]

I'd like also to point to netplan as useful tool above Network Manager and systemd-network as more abstract config and API.