Rework themes support

[jvalkeal]

Original work for theme support was rather naive and handled only basic colouring scenarios. What we should do:

• Support figures so that it's possible use theme to choose between simple character or emoji.
• Add at least one new theme dump which can be used to remove all bells and whistles for less clever terminals.
• Add support to discover theme for a running system like dump theme would be automatically active on CI envs or i.e. if user uses NO_COLOR.
• What would be nice is to also rework some interactive commands as they kinda relate to dump terminals where non tty envs shell would never get any physical user input. This though is probably for another issue.