Review and clean System Designer codebase

[ecarriou]

• [x] Simplify build scripts
• [x] Create State class to that contains all the state properties of the Designer
• [x] Create SystemFactory class that contains all the methods to manage a system creation
• [x] Replace Server class and use _Channel instead
• [x] Create Router class
• [x] Remove platform systems
• [x] Simplify use of JS / JSON in systems

[ecarriou]

Continue refactoring.