[Options] distinguish stage output for CLI and GUI. Simplify options

[mm4rks]

Proposal

Currently we have the option to show stage output in GUI tabs and/or print them as ASCII, giving rise to the following entry in default.json:

...
    "stage_output": {
      "default": "none",
      "title": "Show stage output",
      "type": "string",
      "enum": ["none", "tabs", "ascii", "tabs_and_ascii"],
      "enumDescriptions": ["None", "Tabs", "ASCII", "Tabs + ASCII"],
      "description": "Select how stage output should be displayed.",
...

Do we really need to print ASCII when we use the GUI? Furthermore we can not even show tabs from CLI.

Approach

• change stage output option to: {none, all, list} <-> {[], ["all"], ["list", "of", "stages"]}
• always show starting point (if not none / [] )
• from CLI print ASCII, from GUI show tabs

This simplifies options for stage output considerably.

[mm4rks]

Another idea: Given a stage name, print the previous and the given stage.