[FEATRUE] "Visible Content" feature to item containers

[kreghek]

Problem

There is no method to see difference between looted (means empty) chests and opened (have no closed locks). Now we change isualization after clock on chestview model. But bots can not see difference.

Solution
Add new property enmerable named ContentVisibility. Values:

• Hidden. Persons can't see current content of container. Used b all boxes.
• Visible. Persons see container content. Used by loot bags. Chests changes property value to it when opened once.

Alternatives
Breaks chests after loot. There are no reasons to keep chests after person player open it rigth now (in current version oft he game). But when bot players will build cities then a ability to keep items in some safe boxes will be usefull. This will solved in #1023