Add mobile / wwan panel to GNOME settings

Epic: https://source.puri.sm/Librem5/use-cases/issues/2

As discussed at the settings BoF at GUADEC we want a mobile specific panel for WWAN / mobile. According to Georges Stavracas there already was a WWAN panel redesign but I couldn't find it. @tobias.bernard any idea where that could be?

Somewhat related to #19 (closed)

The minimum functionality is:

select provider
select network
change PIN

Edited May 31, 2019 by Heather Ellsworth

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