[Suggestion/QoL] Ability to fully expand/collapse nested (tree) UI elements

[azaghal]

The game's user interface extensively uses tree-like graphical elements to present the player with nested hierarchies that contain information and clickable elements.

In some cases such hierarchical trees have a tendency to have quite a bit of nesting - like fleets with nested subordinates, or encyclopedia entries.

The game already tries to be helpful in some cases by automatically auto-expanding certain sub-items - like the immediate fleet and station subordinates.

However, in some cases the player may want to be able to manually expand and collapse an entire nested tree (such as nested subordinates or encyclopedia entries mentioned above).

It would be nice if the player could recursively expand/collapse an entire hierarchical tree in the user interface. In case of mouse and keyboard, this could be done when the player clicks on the expand button (+) while holding down a modifier key (CTRL). To cover the joystick/controller input schema, a dedicated input control should be introduced as well.