[CB-3576] Privately signed https links don't work in InAppBrowser

Privately signed https links don't work in InAppBrowser and are blocked
by default on the InAppBrowser. A new option 'validatessl' has been
added that can be specified while
launching the InAppBrowser:

window.open(url, '_blank', 'location=yes,validatessl=no');

Default value of 'validatessl' is 'yes'. This will allow users to ignore
SSL certificate errors caused while opening self-signed https URLs