implement unit breathing

possible side effect of this change:
becaues we are now calling RNG multiple times per frame at depths greater
than 0, any kind of RNG-related reproducability goes rightout the window.
this is a potentially bad thing.

also this will probably need adjustment for varying unit heights.
dead guys don't breathe

granted they're drawn as items instead and as such don't have bubbles drawn
but they may as well not call RNG or anything while they're down as well.
tidy breathing code a little.
speed up base defenses, apply damage ranges, and play more splosions
missed a spot
set BattleUnits' minimum Tu & Energy to 12 during battle.

- else a player could conceivably load up a soldier so encumbered
that moving or even unloading becomes impossible.
Merge branch 'master' of https://github.com/SupSuper/OpenXcom into oXc_kL

Conflicts:
	src/Battlescape/Map.cpp
	src/Geoscape/BaseDefenseState.cpp
	src/Geoscape/BaseDefenseState.h
	src/Savegame/BattleUnit.cpp
	src/Savegame/BattleUnit.h