Add Capability to add Custom Value Variants

[Aymankht]

Currently Value Variants are hardcoded. It would be interesting to be able to add a config file of a DB where custom Value Variants can be defined. This would need a lot of changes to the Core architecture, but I have many ideas to implement this. What are the benefits? Well, the same as with the introduction of geometry's. While geometry's as one of the default Variant most users will leverage, something like 3D tiles or molecular structures are very niche. The implementation of files is something that will allow users to store more complex data, but db computation of this data will still be limited. Creating custom Value variants with their own methods etc. would eliminate the need to adjust data to data types that exist in DB. Rather users will adapt/extend the DB to data types they have.