Experimental feature: study items to become familiar with them.

[brturn]

This is an experimental feature - it is intended to provoke discussion and ideas, not to merge as-is.

This PR adds a "Study" button to the item display page of weapons, armor, and rings.

When studying an item:

• You consume 500 turns of food (or 100 turns if you have the amulet)
• The "use-ID" cost of that item is divided in half
• The first time you study an item it is 'detected' as if by a detect magic potion
• The item can be studied multiple times

The idea here is to ease the play for several situations, without unbalancing the game:

• New players who need some help as they get familiar with the dungeon and want to ID a tool faster. Note that studying an item is always a food-loss in this situation and studying more than one item is likely to lead to starvation (there should probably be a note mentioning this the first time they use it).

• Players that have not ID'd the right equipment yet and suddenly find themselves in a situation that merits immediate equipment sorting. In this case, the food loss is balanced by staying alive in the moment.

• Players gathering a mastery kit, who have already collected the amulet and are now tediously use-ID each item from the vaults on previous depths. Here, the food loss is negligible for the first two 'studies' of an item (since the food would get used anyway as they run back & forth to wear down the clock). This reduces the tedium of collecting a mastery kit, but does not incur significant advantages to the player.