When we launch Ladybird, we currently:
1. Create a BrowserWindow, whose constructor navigates to the configured
new tab page URL.
2. Then navigate to either "about:blank" or whatever URL is provided via
the command line.
This patch removes step 2 and forwards the URL from the command line (if
any) to BrowserWindow. BrowserWindow's constructor then either navigates
to that URL or the new tab page URL.
This will help a lot with developing chromes for different UI frameworks
where we can see which helper classes and processes are really using Qt
vs just using it to get at helper data.
As a bonus, remove Qt dependency from WebDriver.
