Adding REDUCE_SCENT tag to liquid tiles in order to make sure water reduces scent trails

Update from using REDUCE_SCENT tag to WALL tag. WALL eliminates scent over water completely, which makes sense in most cases (like there being no scent trail from sweat or chemical traces left on surfaces) but not all (smoke should be able to waft some distance over water)...

This still has interesting tactical implications: It means suvivors (especially suvivors with Strong Scent) can benefit by ducking in and out of rivers and lakes, jumping in a canoe to avoid being tracked by smell, etc.

* Created new NO_SCENT (json) and TFLAG_NO_SCENT (in-memory) flags
* Updated the scent-diffusion code to use the NO_SCENT flag instead of the WALL flag (the WALL flag no longer affects scent diffusion)
* Left the map-generation and tile-linking code that uses the WALL flag alone (the WALL flag affects map generation and drawing the same way it did before)
* Updated the terrain-types json definitions that previously used WALL to also use NO_SCENT
* Fixed a few tile defintions that seemed like they should have NO_SCENT, REDUCE_SCENT, or be PERMIABLE, but previously weren't
* Updated documentation

…sion across things besides WALLs"

Fixing summary