Remove widget position and use tab_compare instead

issue4092
review13451002
Some tree states fixes

- Direct click on save should also store the tree states
- The timestamp of tree states should be ignored for form view because it is
  only for internal usage
- Store in tree states the index instead of id for new records

issue4130
issue4131
review14431002
Manage field context on Group value

issue4098
review11391004