Prompt template UI changes

A few weeks ago we added a major upgrade to the Prompt Library, with the ability to add specific files, repositories, and other context in saved prompts. With this update we've streamlined the UI in the editor by moving all of the 'current' context buttons like Current File and Current Selection into the @-mentions menu, creating a more natural-feeling spot for all of your context options to live in one place.

This change does not break existing prompts that use cody:// syntax and they will function as normal.