Add WorldBorder support

- Uses API in spigot to get world border
- Blocks faction claims that are outside the world border

Improved border detection

This is the updated border detection, this method is extremely accurate
and does not over partition claim space like before.

Takes the border and divides by two, and then converts the block
distance into a chunk distance.
Ex. Border = 100, Chunks = 6 vertically, 6 horizontally.

We get the absolute value difference between the center chunk and the
claim chunk, for both X and Z. We add both diffs, and if they are
greater than the limit, then we know the chunk is outside the border!

src/main/resources/config.yml

@@ -169,6 +169,13 @@ max-relations:
   neutral: -1
   enemy: 10
 
+# WorldBorder support 
+# A buffer of 0 means faction claims can go right up to the border of the world.
+# The buffer is in chunks, so 1 as a buffer means an entire chunk of buffer between 
+# the border of the world and what can be claimed to factions
+world-border:
+  buffer: 0
+  
 # Raids
 # Allow a faction to be raided if they have more land than power.
 # This will make claimed territory lose all protections