Advantages:
* Code uses common functions for manual usage and automation where possible. This avoids forgetting half of the adjustments like it happened in #14
* Support for meta and wear
* Code duplication for the different automatic modes is reduced/avoided
Additionally, the `techage.item_image` function was adjusted:
* added support meta and wear
* removed duplicate stack size labels for non-tools with max_stack=1
* added optional parameter to "overwrite" stacksize for tools (necessary because of minetest limitations)
9c9dcf8a37