refactor projectile constructor call

put the code in the constructor instead of around the calls to it.
make the vapor probability a ruleset value.
default variable
Merge branch 'master' of https://github.com/SupSuper/OpenXcom into oXc_kL

Conflicts:
	src/Battlescape/Projectile.cpp
	src/Battlescape/Projectile.h
	src/Battlescape/ProjectileFlyBState.cpp
	src/Ruleset/RuleItem.cpp
	src/Ruleset/RuleItem.h