Extending context concept to models

fixes #3275, fixes #3290, ref #3086, ref #3084

- Ensure that we use the current logged in user and not just user 1 when
- removing hard coded user: 1 except where absolutely necessary
- passing context, rather than user to models
- base model has a new function to determine what id to use for created_by etc
Merge pull request #3319 from ErisDS/issue-3275

Extending context concept to models