Restores the display of item techniques.

Fixes #6933

- added output of techniques to item info - only when the technique actually has a name, this allows techniques to be added to items without them showing in the item description.
- added check that any technique associated with an item is actually defined as martial art technique.
- and that's why I added entries for WBLOCK_* DEF_DISARM and GRAB to data/json/techniques.json.

The techniques DEF_DISARM and GRAB are not implemented, I kept them but added "(unimplemented!)" to their name. They should either be removed (from the items and from techniques.json) or re-implemented.

And I removed some outdated and unused functions/member/enumeration, they are not used anywhere.