Add plugin requirement to registries

...java/net/islandearth/rpgregions/effects/RegionEffect.java

...slandearth/rpgregions/requirements/RegionRequirement.java

...th/rpgregions/requirements/RegionRequirementRegistry.java

...a/net/islandearth/rpgregions/rewards/DiscoveryReward.java

.../islandearth/rpgregions/rewards/RegionRewardRegistry.java

...earth/rpgregions/requirements/AlonsoLevelRequirement.java

...islandearth/rpgregions/requirements/QuestRequirement.java

...net/islandearth/rpgregions/rewards/AlonsoLevelReward.java

.../java/net/islandearth/rpgregions/rewards/QuestReward.java