Add "trigger egg capsule" linedef executor

This implements linedef type 464, Trigger Egg Capsule. This allows egg capsules to be created entirely out of linedef executors, and without using the reserved tags 680-682 or the "Egg Capsule" sector type.

Setup:

• Tag: Angle of Egg Capsule Center thing to trigger
• ML_NOCLIMB: Don't end level upon triggering

Test files:

• srb2win-capsule.exe
• capsule.wad