Add 'event.getFrom()' to *some* event. resolves #7

This will allow developers to easily see what Location a player has come from.

As an example use case, I want to get an ApplicableRegionSet at the Location the Player left a region, allowing me to check not only the claim they left, but all others in that location. To do this, I need the Location of the Player when they left the region, which is what this PR is meant to solve.

NOTE: PlayerJoinEvent and PlayerRespawnEvent will pass null as 'from', as there is no simple way to get the players previous location.