Port all entities to lua and convert entity to lua only

[tatjam]

Self explanatory, to be done soon as current entities are vehicle and building, which are really simple. Further entities would be written in lua from the start.

[tatjam]

Kind of done already, some problems that have arised:

• Vehicles must spawn entities, we use a function in vehicle.lua for this so future mods can hook it and add custom stuff to vehicle
• There's a fair bit of boilerplate code to be written in lua

Will close once it's fully done and compiles with a commit.

[tatjam]

Completed.