[AppStream] Allowed chars in the AppStream ID

[Richard Hughes]

Hi all,

I've just tried to launch the URL
appstream://gravatar@jr.rlabs.io.shell-extension from my browser,
which of course doesn't work as it treats the gravatar@ bit gets used
as the login name, and then jr.rlabs.io.shell-extension doesn't match
anything in gnome-software. If we're supporting the appstream:// url
prefix, perhaps we need to limit the allowed chars in the appstream
ID? I'm also using a manual shell-extension as i'm using the ID from
the existing gnome-shell so I'm using a .shell-extension suffix which
may or may not be sane. Converting the @ to _ might be an easy
solution here, ideas welcome.

Richard