Opens the given URL.
Any HTTP URL or relative URL will be opened in a new window.
Modern browser may block any attempt to open new windows, but will usually prompt the user to
accept or ignore. Even if accepted, the decision may be applied to only this attempt, or only
to future attempts. It could also trigger a document reload, causing a session restart.
Non-HTTP URLs like "mailto" will not create a new browser window, but require the client
to have a matching protocol handler registered.