add configuration page to select network mode
explain minimal network usage mode

add a description to network option page explaining meaning of minimal
network mode.
fix logging

Move logging function to correct context and use correct value.
Merge pull request #68 from fferner/populate_network_option_qml

Populate configuration page with a select network mode option
Add the description property for ComboBox with Controls backend

It does not actually do anything yet, but as the Silica ComboBox
has it, it makes it possible to write code that is making use of the
description property without crashing with controls.

The next step will making use of the description property with Controls,
 most probably by just placing a label with the description text under
 the main ComboBox line