Constraints #15
Description
Slots and inventories can have constraints like when and who can use them.
Examples of constraints:
- required class and/or level
- required permission
- any programmatic restrictions like "it should be rainy"
Restrictions should not be applicable only to players because of #20.
It would be also great to have the option fallback for slots. This option should contain another slot id that will be placed instead of the current slot if it does not meet constraints.