SPDX License Identifiers are a more compact / standardized
way of representing file license information.
See: https://spdx.dev/resources/use/#identifiers
This was done with the `ambr` search and replace tool.
ambr --no-parent-ignore --key-from-file --rep-from-file key.txt rep.txt *
We now send out MenuItemEntered and MenuItemLeft messages to the client
when the user hovers/unhovers menu items.
On the client side, these become GUI::ActionEvent, with one of two
types: ActionEnter or ActionLeave. They are sent to the Application.
This will allow GUI applications to react to these events.
