Bumped CPU sharding factor up to 16. Reduced segment size of segmented_vector to counteract increased memory consumption of empty tables.
Forgot to reduce size of two_level_array. That one is actually more important than the segmented_vector.
Well, 8 CPU shards seems like a safer choice for the time being.
Changed an assert into a guarantee.
Merge branch 'next' into daniel_1043

Conflicts:
	src/clustering/reactor/reactor.hpp
Bump serializer version. Changing the sharding factor breaks compatibility.
Merge branch 'daniel_1043' into next