Change bindingTypes from Enum to Custom Metadat

[wimvelzeboer]

The hardcoded bindingType Enum is moved to Custom Meta data to allow additional binding types without having to modify existing source code. It also simplifies existing classes and makes them smaller.

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This change is 

[wimvelzeboer]

@afawcett What do you think of this change? I am thinking about adding platform cache to it, but first wanted to see what you think of this.

[afawcett]

@wimvelzeboer Yeah this looks ok, though the bootup performance and number of queries of this lib is a concern and hence your platform cache suggestion i suspect. @ImJohnMDaniel you have the most experience in the field with this lib and performance, thoughts? The other way of allowing this would be allow injection of new bindings by using an API that gets called from a bound module (the way runtime bindings are added).