Support for proxies with user/pass authentication

[clouedoc]

Currently, the plugin won't work with proxies requiring username+password authentication.

Food for thought:

• add an option to delay the launch of the plugin by X seconds
• instead of fetching timezone information when opening the browser, add a method to Page to do it after the user authenticated the page (and subsequently, the browser). This would require to add an option to the plugin which would state to not fetch timezone informations on browser launch, but wait for it to be called manually.
• add an option to provide authentication informations to the plugin