+ Added more annotations for null safety (developer stuff)
+ Added java doc comments (developer stuff) (don't know if anyone is interested in an online java doc, let me know if you are)
* Fixed issue #70 (GitHub): Signs error
* Fixed issue #69 (GitHub): Critical issue with arenas
* Fixed issue #68 (GitHub): exception error while execution task xxx and problem with voting
* Fixed issue #67 (GitHub): Cannot vote once your own plot has been voted on
* Schedule main scoreboard on join a tick later
* Changed Minecraft version to 1.12, 1.11 is no longer supported