[WIP] Add more expansive Player related events

Adds the following Player events:

- [x] PlayerBedEvent
    - [x] PlayerEnterBedEvent
    - [x] PlayerLeaveBedEvent

More events are to follow as seen fit.

It is, but seems unnecessary since `List` has methods to make it simpler
```java
event.getDrops().add(event.getGame().getRegistry().getItemBuilder() ...);
```
Is neater than
```java
List<ItemStack> drops = event.getDrops();
drops.add(event.getGame().getRegistry().getItemBuilder() ...);
event.setDrops(drops);
```