It is no longer used, so remove.

Build the manifest for stable, beta and nightly in the package step.
This avoids the need of a rebuild to publish the firmware on a
different channel.

Just always default to the stable autoupdater branch. Just because
someone uses a nightly or beta image doesn't necessarily mean we
should also push them to that update channel.  If a user wants to
change, they can still do so in config mode.

update to v1.7

See merge request !7

site.conf: add signing key for 0x4A6F

See merge request !5

Fix link to website

See merge request !4

see <https://blog.sparksuite.com/7-ways-to-speed-up-gitlab-ci-cd-times-29f60aab69f9>

CI: cache only downloads

See merge request !3

CI: explicitly specify what to cache

See merge request !2

CI: take GLUON_BRANCH from build environment if specified

See merge request !1