UDMF: Sector fields

Based on !1694 (merged), so merge that one first.

This branch deals with sector fields:

• The flags field is now exposed to UDMF. This means you can set all the flags that used to require linedef type 8 directly in the sector.
  • The "intangible to the camera" sector special and the heat wave linedef effect have been turned into sector flags.
• The special field has been made obsolete and replaced with the following:
  • damagetype for, well, damage types. There are different damage types for fire and lava: They're identical when applied directly to a sector or a solid FOF, but for water FOFs, lava is solid whereas fire is not.
  • triggertag, triggerer and the sector flags MSF_TRIGGERLINE_MOBJ and MSF_TRIGGERLINE_PLANE for linedef executor triggering.
  • specialflags for everything else. This means you can now freely combine sector effects that used to be in the same group.
• A few sector specials are deprecated and aren't accessible in UDMF.
  • Ring drainers and the egg capsule can be recreated with linedef executors.
  • Bouncy FOFs are now made with the "make FOF bouncy" linedef type.
  • The Special Stage requirements and global gravity sector types are obsolete now that we have level header options for those.
• The Wind/Current and Conveyor Belt effects no longer have to set in the map. The game detects pusher/scroller effects at runtime and adds the flags for you.
• Linedef type 540 has been replaced with a friction sector field.
• Linedef type 1 has been replaced with a gravity sector field and the MSF_GRAVITYFLIP sector flag. You can change a sector's gravity at runtime with the new linedef type 469.

srb2win-sector-fields.exe