woob.browser.url: add timeout parameter
Allows the following:
class MyBrowser(PagesBrowser):
BASEURL = 'https://example.org/'
TIMEOUT = 10.0 # Default value from Browser.
my_page = URL(r'my_page')
my_other_page = URL(r'my_other_page', timeout=20.0)
class MyChildBrowser(MyBrowser):
my_page = MyBrowser.my_page.with_timeout(20.0)