fixed micro missiles

inherit velocity

- Buffed railgun projectile speed by 25%

- changed flechette gun model to hl2 shotgun

- Implemented some solutions which will hopefully make it easier to use projectile-based emplacements on moving vehicles
-- Flechette Gun, RMML, BGL-U and Incinerator's projectiles now inherit a fraction of emplacement's velocity
-- Railgun, Rocket Launcher and Burst Missile Launcher get a bonus to launch velocity after surpassing certain speed. This is done to preserve 100% accuracy
- Removed some unnecessary checks when dealing damage, so all entities should be damaged correctly now
- Slightly buffed railgun so the instakill is more consistent

- Burst Grenade Launcher - Universal now fires grenades in a burst instead of all at once
- Railgun projectile now idly damages everything around while flying to hopefully make it less of a glorified rocket launcher
- Railgun projectile now has a flying sound