💡Toolbox hidden option

[hata6502]

1. Describe a problem.
   I want to load a deprecated blocks, but they are also displayed in toolbox.

2. Describe the solution you'd like. Mockups are welcome.
   By adding hidden option to toolbox, the tool is registered to Editor.js, but it is not displayed in toolbox.
   It's block can be loaded through only OutputData.