26147 mari polish

- Addressed code review comments from previous pull request.
- Loader actions are suppressed when creating a new project.  Previously it was possible to perform actions defined for the loader when creating a new project in Mari - this has been disabled.
- Double-clicking on a publish in the open-publish dialog now performs the open action.
I'm disinclined to add a specific comment here that may get missed if we add ptex support later (as these flags may well not change).  This should definitely be highlighted in the docs though...