Add PNG artwork for WiFi encryption type.

Signed-off-by: mvglasow <michael -at- vonglasow.com>
Restore two-column layout for radio networks on wide screens

Signed-off-by: mvglasow <michael -at- vonglasow.com>
Prevent crash in main activity's onStop() handler, fixes #27.

Signed-off-by: mvglasow <michael -at- vonglasow.com>