connectors: Add support for screw terminals

[dbrgn]

Library PR: LibrePCB-Libraries/LibrePCB_Connectors.lplib#13

Add screw terminal symbols / components.

For inspiration, I looked at the KiCAD symbol:

This looks quite nice, but we cannot replicate it because the pin labels are not yet movable.

This leaves us with two options:

A: Move the screw circle to the right, re-using the line

The circle is very small though and does not really resemble a screw.

B: Make the symbol wider

By making the symbol wider, we have room for the screw on the left side.

I chose this approach. To ensure consistent alignment with other pin headers/sockets, the rectangle expands to the left, it is not centered. This means that you can replace a pin socket with a screw terminal without the wires moving in the schematic.

Here's the final symbol:

[ubruhin]

Nice! But why not simply make the line shorter?

Then the outline is the same as for the other connectors. And with LibrePCB 0.2 we could then either move the text very slightly to the right or out of the symbol to improve the look a bit (although I'm not sure about moving it of the symbol since then it would be inconsistent to all the other symbols...)

[dbrgn]

Hmm, I think that should work as well. I'll try to fix it.

By the way, any preferences regarding terminology, screw terminal vs terminal block?

[ubruhin]

I rebased the branch and slightly adjusted the symbol layout, now making use of the LibrePCB 1.0 feature of specifying a custom pin text position 💪

From my point of view, this is now ready to merge.

[dbrgn]

Awesome, looking great now! I'll check it again, and will then update the associated library PR.