Load creature sounds when transforming

Closes #354
Introduce AvatarStatBlock class.
Convert the user interfacing classes to use the AvatarBlockStats class.
calculate derived stats on the fly instead of caching those.
Move hero_cooldown to AvatarStatBlock.
Entity has a StatBlock pointer now.

needed to fit in the subclasses.
Merge remote-tracking branch 'mainline/master'

Conflicts:
	src/GameStatePlay.cpp
check for array bounds correctly

npc_id must not be -1 when being used as an array index.
Merge pull request #376 from stefanbeller/bugfix1

check for array bounds correctly.
Merge remote-tracking branch 'mainline/master'

Conflicts:
	src/GameStatePlay.cpp
Fixes member initialization order which solves the build warings.
Fixes issue with if tests and orders.
Added member initialization to missing variables in MenuNPCActions
Added member initialization of npc in contructor.
Default value for Avatar::loadSounds() param
Merge remote-tracking branch 'upstream/master' into bugfixes
Made StatBlock dtor virtual.
NPC::loadSound(filename) was shadowing a member variable.
Merge pull request #378 from stefanbeller/master

Starting to cleanup the StatBlock class.
Merge remote-tracking branch 'upstream/master'

Conflicts:
	src/GameStatePlay.cpp