[Enhancement] Command rework

[funaydmc]

The plugin's current command system is actually outdated. The absence of any completer makes using the plugin difficult.
I propose implementing the CommandAPI to rebuild the entire command system.
Of course, existing command will temporarily not be deleted and will exist in parallel with the new one.

[Travja]

Tab completion was added here db87519

[funaydmc]

I guess I missed this dev build. it's amazing
However, what I'm aiming for is not only tab completion.
There are also entity selectors, real time command error indicators ...ect
Another problem is that all current commands are /class. This will make it difficult for both development and use. Logical grouping commands will solves this problem

[Travja]

Yeah, in that regard, commands could use a decent amount of work

[goflishMC]

@fructozer are you wanting to do that project to use logical grouping? feel free to start if you do. If not that command rework is on our to do list, I just don't have an ETA for it as it's not top priority at the moment.