Only data providers can dragged on the Provider field of a data binding that provide the correct data type

[Christian Oeing]

This would require a hint on the data provider as well about which type it provides

It should be possible to use a data provider which data can be cast to the desired type.

This issue is the remaining part of issue #17 that introduced data type hints in general.

[Christian Oeing]

Added possibility to add data type hint to provider and using it to filter components when dragging game object on to data binding provider