TTY: Add compile-time option for tile data hinting

TTY: Add compile-time option for tile data hinting

Several people have asked if 3.6.0 supports playing with tiles on
a public server. Because there's no way for the user's end to know
what that white @ is, this adds special console escape codes for
tile hinting.

The idea was originally a patch called TelnetTiles by Justin Hiltscher,
but this expanded version comes via NAO, where it's been in use for years.

This is basically an interim hack, which should go away when/if
we support actual client-server model.