Enhancements on the source code and the command manager

 - [x] Added Javadoc everywhere.
 - [x] Improved the style of the source code to a more readable, clear style, with more spaces.
 - [x] Added some comments.
 - [x] Added some spaces.
 - [x] Removed useless things (like `if(var == true) {}`).
 - [x] Added visibility on all methods.
 - [x] Externalized the CommandExecutor.

This is an early Pull Request. Don't merge if the entire list is not checked.