TLS certificates for LoRa App Server will become optional

In the next release of LoRa App Server, the TLS certificate configuration will become optional (it will still be possible to add a TLS certificate if needed). See also: https://github.com/brocaar/lora-app-server/pull/235. This means it is no longer needed to generate self-signed certificates / deal with browser warnings, meaning less complexity during the initial setup :slight_smile: