Add preferences menu option to turn weather off.

In both English and German clients.
Add small amount of x velocity to snow.

Recommendation from Keen.
Rain/snow refactor, particle effect bugfix, CV window transparency.

Refactored the code for rain/snow and made a lot of adjustments.
Fixed a bug that was preventing random particle position from being
truly random.
Made the windows in CV main room properly transparent so weather effects
happening outside can be seen.
Handle effect changes correctly.
Add msg to remove a changed texture.
Add wreath texture and snow changing code to Qormas.

Qormas now changes the texture on doors (to add textures with wreaths)
and also calls StartSnow in room.kod if necessary which handles snow for
that room. EndSnow removes it.
Add sector/sidedef IDs for placing xmas decorations.

ID 15 is for sidedefs that require a snow texture, Sector ID 10 is for
water which doesn't get snow, IDs 21-34 are for door texture changes.
Add water effects and ice texture.

Use the new protocol to change water into ice (no scrolling, no depth).
Added a new ice texture to place on the water.
Fix sector IDs
More snow particles.
More tagged rooms.