app: Add sensors_lorawan_se example app

[azerimaker]

Summary:

Adding a new app which uses the Secure Element for LoRaWAN comissioning. This app is the main demo app that's shipped with the device. DevEUI's are printed on the back of each device, and using the QR codes users can easily claim a new device in their TTS app console.

Fixing a small bug related to the TCXO voltage setting. Closes #241 , #151, #152

Changes:

• Added a new demo app: /sensors_lorawan_se
• Fixed the TCXO voltage setting
• Added handling to avoid NULL values from corrupted sensor readings

Notes for Reviewers:

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Release Notes: (optional)

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