Improve moOde code base

I find the current moOde code (php backend and javascript frontend) hard to read and error prone, due to very large files, long functions, lots of duplicate code and lack of unit tests and documentation.

Improve readability & maintainability

• make functions shorter by splitting them into new shorter functions
• split large files into shorter files
• remove code duplication
• convert magic numbers/strings to constants
• refactor into classes
• unit test
• document
• better error reporting (or is it good enough?)