after the multiskin / 3d_armor mod did own initialization

Closes #18

13 new skin parts

Add SFINV support

* replace deprecated function calls

* update mod.conf

https://forum.minetest.net/viewtopic.php?t=16079

Each login an custom private skin is registered in skinsdb that needs to be cleaned up on logout.
The issue #15 is timing issue that uses the old skin that does refer to the not existing player object in skin_indexes.
By the way, the skin_indexes[player] needs to be cleaned too.

* Support for skinsdb. The character_creator is "selectable" as a skin from the list

* license sting added to skin metadata

* Multiskin support (for 3d_armor 0.5.0)

Retains compatibility for older Minetest releases and older releases of 3d_armor. Added check for multiskin - which is found only in 3d_armor 0.5.0. If multiskin is present, it uses that. Else, it uses 3d_armor or falls back to set_texture

* save data after every skin change, since on_shutdown is not fail safe
* remove unnecessary saving of data on shutdown

Add mod.conf

Add description.txt

This file will help clients to list and determine mod content.

This will help clients to install and maintain mods in the long run.