Implements two new keys for controlling if a unit with `TiberiumHeal=yes` spawns a Tiberium patch when it dies.

[CCHyper]

Closes #580

This pull request implements two new keys for controlling the Tiberium spawn feature only when a unit with TiberiumHeal=yes dies.

[TechnoType] TiberiumOnDeath=<boolean> - Does this unit spawn a Tiberium patch when it dies? Defaults to yes.

TiberiumTypeOnDeath=<TiberiumType> - The type of Tiberium this unit will spawn when it dies. The value here should be the same as the name of the Tiberium types section (e.g. Riparius). Defaults to the first entry in the [Tiberiums] list.