Kaiso

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Cache descriptors for static types.
Cache all descriptor properties.

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Fix indexes when type of instance is changed.

Don't pin version of iso8601 library, allow future versions as well.

Applied attempted workaround for intermittent " UNNAMEDx" issue seen in earlier
releases of Neo4j 1.9 server.

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Add `Manager.get_by_unique_attr` to bulk load objects given a list of values
for a unique attribute.

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Bugfix: `change_instance_type` now creates the correct properties with the
new InstanceOf relationship.

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Addressing performance issue in `_conver_value()` which issued unnecessary
http requests for getting node propertiest.

Removed the need for relationship objects to have start and end attributes
when saving.

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Bugfix: Allow deletion of types with no attributes.