Fixes: #478
Add new --allow-insecure-http flag to support the use of HTTP URLs.
This is needed to allow swupd to download content from http sites;
generally development mixes.
Also enable the use of the setting in both the TUI and GUI to allow
the user to set a swupd mirror which is HTTP.
Signed-off-by: Mark D Horn <mark.d.horn@intel.com>