Smooth item throwing and make them stick for a while; Fix not equipping the right item from the inventory; Introduce isDirty for db-entities

* Item throwing was rather weird, and the items weren't actually added to the world.
* Fixed removing items from inventory to be by id when possible.
* Cleaned up a little on item use/equip/remove usage - now more intuitive and less player/inventory sync concerns.
* isDirty ---- objects that extend db-entity has a new property isDirty - should be 'true' in order for a .save() to actually take place.