Create item

[Ekhorn]

Description

As a user, I want to be able to create items, so that I can make notes.

Acceptance criteria

• To create an item, the user must be able to right-click within the viewport to open a contextmenu that allows creating an item at that location.
• Alternatively, the user must be able to upload an item, by dragging over a file or by selecting upload instead of create from the contextmenu, which places it in the middle of the screen.
• An item must be persisted by coordinate to the database and retrievable.