General improvements to the schematic designer

[Matrix89]

While trying to use the schematic designer, I've noticed that it's missing some QoL features, one of which was copy and paste, I've already implemented it, but I still have some other ideas I need more feedback on thus I'm making the PR a draft.

The features I'd like more feedback on are:

• Moving the buttons on the top left off the design screen, currently they cover a bit of the canvas when you want to build in the top left corner
• Ability to assign shortcuts to elements, the way I see it, is that you can press a number while hovering on an element in the element selector to assign it to a specific number key
• Ability to pick elements using the middle mouse button
• Ability to export/import schematics and copied regions
• Ability to stack the copied region like in world edit
• Replication of other people's cursors when viewing the same schematic