Optimize GameRules to use LinkedHashMap

[Spottedleaf]

Previously TreeMap was used which has poor get(K) performance.

Using LinkedHashMap we can get the performance benefit of HashMap and the iteration order given by TreeMap.

[killme]

Doesn't this change the iteration order?
LinkedHashMap is by insertion order, TreeMap is by key order.

[Byteflux]

Doesn't this change the iteration order?
LinkedHashMap is by insertion order, TreeMap is by key order.

The order of the original TreeMap should be preserved since the entries in the tree map are being added to the LinkedHashMap using putAll(treemap).