i3: Remove mod+cursor keys bindings

I want these keys for something more useful, and besides - If you aren't
using mod+hjkl, you're doing it wrong (as in, you're moving your hand
way too far and limiting the benefit you get from using a keyboard
driven window manager).
i3: Add mod+up/down bindings to adjust laptop backlight
i3/randr: Fix backlight adjustment to work with more drivers

Use all four bytes from the backlight integer from randr to work with
drivers that have a backlight range of >= 255. It would be nice if
python-xcb did this automatically (or am I just doing something wrong?),
but at least now I understand why I got multiple values in the first
place.

Also change the default backlight deltas to 5% instead of 1 unit - the
intel_backlight driver has a range of 4437, so bumping that 1 unit at a
time is not very useful.
i3/thinkpad: Stop forcing outputs to LVDS1