Create mix models in Brainstorm server mode

[rcassani]

Currently, the creation of mix models depends on the code and controls in panel_scout. However these are not created when Brainstorm is started in server mode (completely headless).

It is necessary to refactor some functions to generate mix models without the controls of panel_scout.

For the moment, the DBA tutorial script (tutorial_dba) is restricted to run in Brainstorm with GUI or with hidden GUI (nogui mode). Commit: 3467b20