Rename models.js to

The file no longer refers only to models.js original file but too db.js file, so the new name makes more sense.
Split js code

The products_pos.js file is replaced by a main.js file that imports the rest of js files, each one with a piece of funtionalitiy:
  - db.js: database related overrides
  - models.js: overrides same file on PoS
  - screens.js: add new code to implement menu screens
Remove traduction and code clean

Remove traduction to avoid field no defined errors.

Remove screen.js code not overriden
Access Model

New access rights to r/w in pos.type model