Shot Lua API update + related internal changes.

With this change, shots are no longer stored in a std::list.
In the current code, the global shot store may be modified while iterating,
this did not cause problems with the list implementation,
but would easily crash if a shot is removed while iterating.
To fix this, a 2nd vector stores shots to be deleted from the global store
and does so when no iteration is in progress and modifying the vector is
safe.

Added functions:

getFirstShot -- for iterating over all shots on the map
getNextShot
shot_setFirer
shot_setExtraDamage
shot_getExtraDamage
shot_getDamage
shot_getDamageType
shot_getName