Bug fixes

Fixed #63 - Issues installing package groups
Numerous edge cases in examples/guided.py where some default options caused KeyError at certain points if left empty.
Empty locale (very first question) caused a hang because loadkeys will enter some form of interactive mode if no option is given.

New features

Added a Systemd and Networkd handlers (based on Ini() class), which is a basic helper to create INI files for Systemd services and network configurations.
Added Installer().configure_nic() which helps to set up a interface inside a installation. (in the long run, perhaps add a similar thing to the live medium?)
- Supports DHCP and static IP configurations (limited, but there are two options at least)
- TODO: Show current IP-address to make it easier to evaluate which interface to configure