Type declaration for ESB mods API

![image](https://user-images.githubusercontent.com/13326808/67152123-533f6780-f2d9-11e9-84db-c623eb136bf3.png) ![image](https://user-images.githubusercontent.com/13326808/52314225-d7a7bf80-29c2-11e9-9664-81286c1db919.png) Remark: `This project is part of a closed project ElementarySandbox` [![Maintainability](https://camo.githubusercontent.com/4904b42c619e0efb7083c6537ba3cd05ba637e63/68747470733a2f2f6170692e636f6465636c696d6174652e636f6d2f76312f6261646765732f66663162346365346230303938303538663237312f6d61696e7461696e6162696c697479)](https://codeclimate.com/github/0xF6/ElementarySandbox.typing/maintainability)