* Add Option to Control HTTP Scheme
Once certificates are installed renewal should always use HTTPS.
HTTP is only required if there have never been any certificates on
the device.
This also fixes an authentication issue where HTTPS is forced
by the device. Before this patch authentication failed for
devices which forced HTTPS because the POST request used
for request did not follow the HTTP to HTTPS redirect.
* Use http as Default Scheme
Using https as default for SHELLY_SCHEME breaks existing deployments
as they may not have a SHELLY_HOST which is identical to a name in
the certificate.
SHELLY_SCHEME is now a parameter as any other without the automatic
upgrade to https. This will always need to be done manually.
