JUMP_TAG candidates

[gribbet]

• Waypoint candidates are now indicated with a JUMP_TAG and the waypoint generation has been adjusted accordingly
• Added an SA_AUTO_SELECT param to enable waypoint candidate selection without enabling mission generation
• Added some SIM params to specify initial drop velocity and direction

To test this locally, I've had to disable the override behaviors in SA_GD2000::input_mixer. With the current behavior the sim seems to crash straight down into the ground.