Slight Tweaks to the purge sectoid, and purge sniper.

Elite Purge Sectoid's got two buffs for their psi abilties.

Purge Sniper now has the ability to detonate Xcom units grenades.

Lowered purge sniper HP by 1,
Tweaked the Purge Vanguard AI.
Tweaked drops of the sniper cyborg and vanguard units.

1. Localization changes
2. More Purge units are able to be harmed by poison now. (Except cyborg and MEC.)
3. Purge MEC is now slightly more resilient. (they no longer take even more damage from electrical attacks. They take as much damage as other robotic units from electrical now instead of having an even bigger weakness.)

Typo fixes for localization.

Lowered spawn weights of some of the units.