Unified handling of battle sides ID's

- Replaced BattleSide namespace-enum with enum class
- Merged two different BattleSide enum's into one
- Merged BattlePerspective enum into BattleSide enum
- Changed all places that use integers to represent battle side to use
BattleSide enum
- Added BattleSideArray convenience wrapper for std::array that is
always 2-elements in size and allows access to its elements using
BattleSide enum

lib/battle/CObstacleInstance.cpp

@@ -52,7 +52,7 @@ std::vector<BattleHex> CObstacleInstance::getAffectedTiles() const
 	}
 }
 
-bool CObstacleInstance::visibleForSide(ui8 side, bool hasNativeStack) const
+bool CObstacleInstance::visibleForSide(BattleSide side, bool hasNativeStack) const
 {
 	//by default obstacle is visible for everyone
 	return true;
@@ -134,7 +134,7 @@ SpellCreatedObstacle::SpellCreatedObstacle()
 	: turnsRemaining(-1),
 	casterSpellPower(0),
 	spellLevel(0),
-	casterSide(0),
+	casterSide(BattleSide::NONE),
 	hidden(false),
 	passable(false),
 	trigger(false),
@@ -148,7 +148,7 @@ SpellCreatedObstacle::SpellCreatedObstacle()
 	obstacleType = SPELL_CREATED;
 }
 
-bool SpellCreatedObstacle::visibleForSide(ui8 side, bool hasNativeStack) const
+bool SpellCreatedObstacle::visibleForSide(BattleSide side, bool hasNativeStack) const
 {
 	//we hide mines and not discovered quicksands
 	//quicksands are visible to the caster or if owned unit stepped into that particular patch