Allow all leaves to be recoloured using event

Modifies the GetFoliageColor event to add an identifier for different types of leaves. Standard identifiers are oak, spruce, birch and jungle. Tested and appears to be working.


Sample code:
```java
    @ForgeSubscribe
    public void onFoliageColor(BiomeEvent.GetFoliageColor event) {
        if (event.identifier.equalsIgnoreCase("oak")) {
            event.newColor = 0xFF0000;
        }
        if (event.identifier.equalsIgnoreCase("spruce")) {
            event.newColor = 0xFF00;
        }
        if (event.identifier.equalsIgnoreCase("birch")) {
            event.newColor = 0xFF;
        }
        if (event.identifier.equalsIgnoreCase("jungle")) {
            event.newColor = 0xFF8800;
        }
    }
```