[2020] Map editor

It works, its not overly easy for newcomers, but we can continue to improve based off feedback.

++ Create blocks, set block types and textures ++ Modify terrain, size dimensions/shape, paint terrain, flatten ++ Add props, set prop dimensions, rotation, position, color/mask (some), hide props +- Browse editpad for textures, props and other entities +- Change entity properties via editpad +- Add pickups, set time until its next spawn after being picked up ++ Add liquids, set color, size, damage value every 0.5 seconds +- Ability to set moving props, including volume triggers, shootable triggers, movement speed ++ Add jumppad, set direction and strength ++ Add teleporter, set target and exit speed +- Add spawns, set team, area (for arena duel), other properties +- Add lights, set type (point light, diffuse point, spotlight, spotlight+volume, ambient, ambient node, fog, vertical fog), radius, intensity, color, visibility function (like blinking) ++ Add billboards ++ Intro and MVP showcase cameras +- Sound entities +- Particle effect entities +- Symmetry function +- Editing controls +- Editpad