Massive cleanup

[IllusionTheDev]

Hey there, we use this at work. Spent ~90 minutes cleaning this up, here are the steps I took:

• Renamed every field, method and class named_like_this to meet java's standard styleguide

• Replaced the exposed mutable maps with a facade class, and made a class to encapsule all mutable player data

• Reworked the command argument enum slightly to apply predicates instead of manually checking in the main command block

• Reworked the command classes to apply guard clauses instead of nested if statements

• Fixed a memory leak by removing player data upon player quit (Might still need to cancel any camera tasks)

• Command tab completion isn't fully hardcoded anymore, which means you don't need to update your tab completer when adding a new subcommand

A few more changes I have in mind:

• Split CameraHandler into a CameraTemplate and CameraView, which allows us to pre-compile camera paths without player context, improving performance both in CPU (less computing) and RAM (less duplicate objects)
• Rework your config system to read and cache the fields rather than fetching from the FileConfiguration object in runtime, ensuring a stronger immutable design
• Rework the hard-coded messages into a lang.yml file

[svenar-nl]

This looks really impressive. It has been a while since I worked on PowerCamera. I'll take time to look over it and test it.

[IllusionTheDev]

@svenar-nl Have you had the time to look at it yet?

[svenar-nl]

It took some time to look at all changes and getting used to it, but it looks well structured. I have some other changes planned to ease development later on, so I will accept this pull and continue work on it (besides my other plugin PowerRanks).