* Retain backwards compatibility with legacy capybara-webkit API.
* Confirm dialogs are accepted by default; dialogs are dismissed.
* Legacy API overrides the default action, and does not raise errors
for unexpected modals.
Turns Response into a QObject and sets parent to the
command that emits it.
Each Command is also a child of the decorator commands,
Timeout and PageLoading commnds, so that deleting the
top level command will delete all the children.
See discussion in #430.