Add waiting, window closing and page switching options to withNewWindow()

[geb-bot]

Originally created by Marcin Erdmann.

And also throw an own exception when no window has been opened, now it looks like web driver is throwing the exception which is not the case.

[geb-bot]

Originally posted by John Murph.

Just a comment on the page switching options. On the mailing list, Luke suggested this syntax:

withNewWindow({ /* opening action */}, page: SomePage) {}

Also, after the window closure (the body) returns the context should be automatically switched back to the calling context.

[geb-bot]

Originally posted by Marcin Erdmann.

Fixed in geb/geb@5749221

[geb-bot]

Resolved