ConnectionSettings: Allow creating a connection from MeCard data

For connecting to a network by scanning a QR code. Connection code is lifted from QRCA with MeCardParser in Prison.

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@vkrause @grulich @sune

I modeled it after the existing fromMap, so the caller is responsible for creating the relevant settings object and setting a UUID:

using namespace NetworkManager;
auto settings = ConnectionSettings::Ptr(new ConnectionSettings(ConnectionSettings::Wireless));
settings->setUuid(ConnectionSettings::createNewUuid());
settings->setAutoconnect(true);
settings->fromMeCard(m_parsedContent); // <-- You are here.
NetworkManager::addConnection(settings->toMap());

See also prison!38 (merged)