Glass bottles need equivalent of FillBucketEvent

Currently mod liquids tend to use Material.water, which means right-clicking a glass bottle yields a water bottle. Buildcraft oil is one example. Would be nice if glass bottles got the same treatment as buckets. Couple of options:

 1. Reuse FillBucketEvent, with the semantic "fill a bucket's worth of liquid into this container". 

 2. Introduce a parent of FillBucketEvent, called FillContainerEvent, and add child FillGlassBottleEvent. This introduces some complexity but the naming is more intuitive.

I'm in favor of choice 2. I'll submit a PR if this is deemed acceptable.

As an alternative or in addition, we could revisit the whole custom bucket approach. Now that we have FluidContainerRegistry, it is possible to handle the filling of containers generically.

Moving these fields breaks all current mods that use this event.