Add "walk bot" script

[beforan]

We want a script to randomise features of our afternoon walk break.

• which direction to walk (clockwise / anti-clockwise)
• which staircase to use going and/or up
• triggered manually? or from slackbot's "walk" reminder?

Ideally i guess this should be made into a generic configurable "randomise things from a list, or several lists at once" script, so bonus points for doing it that way and making it reusable in the wider world. We could probably npm that, unlike a script that explicitly randomises staircases in our building.

[beforan]

Also in future could consider making it dynamically configurable.

e.g. if the config was in (for example) redis, then could add commands to modify lists at runtime

[beforan]

I've merged the first version of this, since in practice production devbot was running from that branch anyway...

However the issue here should remain open as there's more work to be done.

[beforan]

13 is wip, so once complete should allow this to become a way better script