Custom theme on character messes with theme preview

[Jowan-Spooner]

The problem

This behaviour is somewhat expected but far from what one would expect.

If you select a character for the theme preview that has a custom theme set, it won't actually display the theme you are editing but the custom theme of the character.

Because the character is selected at random by default, this can be VERY VERY confusing as described here #850.

Solutions

• Characters with custom themes should only be suggested/possible if it's their theme that is edited.
• Additionally the design of the character selection box should make clear that it is a setting
• The character should either not be random by default or remember what character you set (possible for each theme)

[coppolaemilio]

Made it easier to understand what the character picker is by adding proper styling and changing its position. dialogic-godot/dialogic@b35e439

The fix for the other two tasks are coming whenever I can continue.

[coppolaemilio]

Fixed the first one Characters with custom themes should only be suggested/possible if it's their theme that is edited.
Only the last one needs to be fixed, but I might not include it into Dialogic 1.4.2 since we are already going too over the scope of the update