Refactor UI layers

The main goal of this MR is to solve a problem with UI defined by Lua mods: it can overlap the main menu and console even when using layers intended for gameplay purposes. That is because until now we relied on the fact that any interactable vanilla UI is closed when Esc is pressed, which is also the button to open the main menu.

It was not a very reliable solution, and enforcing it on mods would be strange. So instead I've layered console and main menu on top of the gameplay layers.

The rest of the MR are various refactors and naming improvements. In particular, a big change is that all the modals, which force the player to give an answer and prevent even the main menu from being opened are now in a separate layer. That is a necessary change, as they need to be above the Main Menu layer. There are quite a few windows like that, and I'm not certain I got them all, so this MR will require some testing.