Support multi-valued properties

[peterboncz]

• Spark dataframes can support lists of literal values, so this is easily added on the storage level.
• We should support lists of literal values (list, list, list, list, list, list) in the schema languages and catalog
• This means we should then also support the functionality of binding a property value to a variable. This has the effect of “unrolling” the multi-valued value into individual rows of the new binding table. If the multi-valued values was in fact unbound (NULL), the binding is not lost, but will consist of a single row in the binding table (with the variable taking NULL in that row).