No longer use default_wood.png for one side of the bed head and
one side of the bed bottom node.
Add a new texture for the underside of both beds.

Relicense WTFPL media to CC BY-SA 3.0.
Various corrections and edits.

Part 1: All mods except default and xpanes.
Add license.txt files.
Add missing README.txt files.
Check and update copyright years for all contributors.
Improve text format and make more consistent.

Rename in game.conf and documentation
Update game_api.txt documentation for bucket API and tree functions
Fix tab, space and comment formatting in game_api.txt
Rename in mod READMEs

Add option to disable bed's night skip - Solve second point of #512 by adding a setting, `enable_bed_night_skip` , with default value of `true`.