This is #15 on the github. Improves performance, cleans up the codebase, and adds a QoL command. Due to a version naming issue, this is tagged as 1.2.1-release whereas it should be 1.2.1, however 1.2.1 already exists on spigot due to an issue.

- Removed deprecated spigot api usages
- Replaced global player list with hashmap
- Removed incorrect usages of Stream API (and added correct ones)
- Fixed possible NullPointerExceptions
- Dependency injection instead of global static objects
- Added comments where code is not very understandable
- Splitted one command executor to 3 for single-responsibility
- /manhunt command to see current teams (extracted from /assassin command)
- code cleanup