Add mapping between eDP1 and LVDS1
Retry obtaining EDID for 30s (by default)

On intel Iris 5100 integrated GPU EDID of monitor is available after
some time (~15s), therefore external monitor was not configure properly
(EDID read immediately after UDEV event was empty).

Now screenful will try to read EDID again when empty value was read. It
will give up after 30s and show error notification.
Merge changes from r2d2rogers fork[1]

[1] https://github.com/r2d2rogers/screenful
Merge pull request #1 from dluksza/master

Pull upstream changes.