Parse host domain in config

[robertvanhoesel]

When initializing the SDK with a url that ends with a slash, the SDK won't accept incoming events, as postMessage only contain the origin (scheme + host + port) and not a full url. We do a exact match on the domain set in the config.

new Crowded({
    domain: "https://yourcommmunity.com/" // hostname of the community
                                       ^ will not work
});

We should change this, let domain always be just a domain (without scheme or path segments), prepend it with the scheme ourselves (should always be https) and maybe sanitize the input.