Added Centered Variant for Large & Small ship.

Variant has same build requirements, but can be mirrored correctly, as it's design is not A-symmetrical. It does have it's own LODs, and build states.

Following "voicesinthedark's" suggestion to seperate large amounts of materials into smaller groupings when building the thruster I have done just that.

Thruster components are now broken into 4 groups of 720.

Also added a requirement of a few Interior Components to insure that the model will not appear complete till they are added & welded in.

I would like to point out that I myself have not experianced the game crash that people are reporting, even though I have tried welding & grinding the thruster in survival & creative, with & without ships. I have only done this on a single player, or multi-player with myself as host, so it appears the issue may be related to the server. Either way, hopefully this will fix the issue people on servers have been having.

Increased thruster flame size on large ship thruster.

Thruster damage re-activated, and the thrusters should no longer destroy themselves on large ships.

The issue seems to have been that if there are two collision meshes, it can hit itself, but if there is only one, the flames ignore it.