This adds Semtech LoRa Cloud integration with currently TDOA and RSSI
based geolocation implementations. When using this integration, there is
no need to use the ChirpStack Geolocation Server as this integration
provides the same capabilities without the need to setup an additional
component (the ChirpStack Geolocation Server). This also makes it
possible to let each user use its own LoRa Cloud subscription and
tokens.

Besides the new integration, this commit also contains a refactor of the
integrations in general, to make it possible to let one event handler
(e.g. uplink) publish a new event (e.g. location).

In the near future, this integration will be extended with Wifi and
LR1110 GNSS geolocation capabilities.

This implements the FUOTA building-blocks (remote multicast-setup, app
layer clock sync and fragmentation-session setup) + provides an
implementation of a firmware update engine.

For now, this only implements sending FUOTA deployments to a single
device.

The self-signed certificate is no longer used.

As CGO is only disabled on Docker, we can remve the -a flag which should increase the build speed for non-Docker builds.