New protocol BP_SECTOR_CHANGE to set a sector's depth and scrolling speed.

Changed a function name called by the existing protocol BP_SECTOR_ANIMATE from SectorChange to SectorAnimate. This protocol is currently unused anyway.

Created a new protocol, BP_SECTOR_CHANGE to change a sector's flags. At the moment this can change the depth of a sector and the scrolling speed of its texture.

A new list in room.kod (plSector_flag_changes) keeps track of the depth and scroll speed changes. SetSectorFlags can store changes to sectors (by sector ID number) in this list, which is sent to players similar to the sector animation and texture lists. RemoveSectorFlagChange can delete an element from this list, which restores the original behavior of the sector.