Make resolved entity assertions iterable

[MichaelHirn]

Calling .resolve on an entity (Individual) leads to all (property and assert) assertions being fetched, decoded, and attached to the entity. However, if there is only assertion that has the same assertion property it will be attached like this entity.customKeyAssertionName instanceof Object || instanceof {String|Boolean|Numeric|...} and if there are two or more assertions that share the same assertion property it will be attached like this entity.customkeyAssertionName instanceof Array.

This causes ugly boilerplate when trying to use the value and to fix that we need to make it always return an iterable object e.g. an array. That object may have some helper methods like .getFirst to make it easier to access when there is only a single assertions