Improve "add subcircuit"

[jellebakker96]

No description provided.

[jellebakker96]

Also, should "Add subcircuit" not be called "Insert component" because a device is not a circuit.

[jellebakker96]

"Add subcircuit" does not allow you to add cells from other libraries

Add a symbol for an empty subcircuit. Richt, now it looks really strange in the classic layout, and in Tetris, it is difficult to see (only a gray blop).

Think about removing the one port because an empty subcircuit/component does not have any ports.

It is unclear to me what that "edit" button does because when you click it it seems like you enter a new subcircuit but then how should you give it a name and how can you see it in the library editor?

[jellebakker96]

Maybe also change the location of "add subcircuit" to the top of the sidebar because that one is the most versatile of all the "add component" options.