Add an "all-available" Civilization

[PatataMaxtex]

It would be nice to have an all-available Civilization to be able to show the techtree without any techs and units crossed out. This would be helpfull to show beginners all the units and techs at once. This might be even better with an option to (not) show unique units and techs.

[HSZemi]

While that is technically possible to implement, wouldn't that also confuse beginners, since they would be looking for the all-available civilisation in the game and not finding it?

Sadly, we currently do not support a dynamic tech tree layout, so hiding unique units and techs would only leave gaps. Besides: A castle without unique units and techs sounds just odd.