Improve Command and ConsoleCommandHandler classes

* Improvement in general
* Remove some pointless stuff, and some methods like `getCommandByName`
and `getCommandName`.
* Improve help command and make it get all commands automatically (no
longer need to add command-by-command to help command)
* using `switch` rather than `String.startsWith` in
`ConsoleCommandHandler` class
Delete Blocks, Remove duplicates in BlockType

* Delete Blocks enum
* Remove a duplicate constant(`CAKE_BLOCK`) in BlockType enum