Fully redone Sales Processes Workflow doc

Some references are commented, as the referenced doc aren't merged into the project yet
We don't need a custom directive. You can write it like this:

```rst
.. figure:: ./img/sales_process_workflow/Screenshots/WorkFlow.png
    :width: 100 %

    fig.1 "Sales Processes" workflow diagram
```

Styling the caption is then simply adding some custom CSS to the Oro template.