Experimental feature; screenshot with item descriptions when using stairs

[brturn]

This is an experimental feature for remembering the state of previous depths and the items left behind when the player uses the stairs.

THIS IS A TOTAL HACK - not intended for merge, just ideas and discussion.

Before taking the screenshot, the sidebar is updated to display the number of (Food, Life, Strength, Enchant) found on that level, as well as a compact list of the items which were left behind (eg. from vaults, or due to porting).

Screenshots are named by Seed, Depth, and Turn, such as "S364151339 D1 T532.png" so that when traversing the levels more than once, an accurate record is kept of the latest state of each level.

This experimental implementation is cheating, as it displays the number of (Food, Life, Strength, Enchant) which was generated and placed on that level, rather than the number discovered. But I just wanted something quick to test out.

Possible improvements:

• Separate the items from different vaults so the player can see which item choices exist among the vaults in that level
• Once item names are discovered, the screenshots are not updated (they are static), so a "lavender" potion left on level 4 does not update after it is discovered to be a caustic gas potion when used on level 5.