i3-config: Working solution for remapping Caps Lock

This is a correction to ea18345b that had two issues:
- The remapping wasn't persistent.
- The command to clear the lock didn't always work and therefore Caps
  was occasionally remapped to Escape with the lock on.

caplockoff.py is stolen from
https://github.com/zfogg/zfogg/blob/master/bin/capslockoff (thanks).

The new way of remapping Caps changes the output of `setxkbmap -query`
thus the change in the keyboard layout toggle command.