Eliminate OOUniversalID

[JensAyton]

All uses of OOUniversalID should be replaced with OOWeakReferences.

Quite a lot of this has already been done in 1.x and in Oolite2. Relevant Oolite2 commits:
cebfbda Killed me some OOUniversalIDs.
29f976b Converted ship primaryTarget from universalID to weakRef.
ee02960 More universalID -> weakref fixes.
0050786 Changed AI foundTarget from universalIDs to weakRefs