Meteors redux

__Fixes and changes to meteors waves to make it more threatening.__

* Fixed meteors not properly qdel'ing (fixing infinigibs or infinisplotions) and variables initialization. Admin-spawned meteors should not instaqdel anymore (fixes #5226)
* Meteors are more threatening : they now more oftenly get inside the station and bust any non-dense tile they move into (present objects are hit with the full force of the meteor).
* Three types of waves, chosen at random when the wave is created : normal (mostly medium meteors), threatening (a lot more big, flaming and irradiated) and catastrophic (mostly big meteors, with a very low chance to spawn the station buster Tunguska meteor)
* Medium meteors no longer explodes when it was intended for big ones
* Meaty Ores now splat blood on turfs instead of busting them (Xeno splat xeno blood)
* Reinforced girders now have their own ex_act proc. Regular girders are then less resistant to explosions.

The whole thing is still largely dependant on RNG, with sometimes rwall being torn down by medium meteors, some other times big meteors exploding on reinforced girders without even getting inside the station (ex_act haphazardness being the main cause).