cache.vertices = true causes failures

[Pieter Martin]

Sqlg implements an optional transaction scoped cache of vertices.
The idea was that a user will then reference the exact same SqlgVertex in memory.
However it defaults to not caching vertices and the tests have not executed with the cache on.
Turns out it causes subtle bugs.

Going to remove the cache, it will be up to the user to not have multiple SqlgVertex pointing to the same vertex in the db inside a transaction.

This will unfortunately cause subtle bugs itself in user's who used the cache.