Submarine interior overhaul

The submarine's interior has been reworked with new textures and custom lighting.

Map & objective changes

All of the old objectives have been reworked or replaced to better match a consistent overarching theme, which the map has also been changed to follow.

QoL changes

As requested, I have added an option to operate the submarine without having to point at its controls. This option is enabled by default and is called "No cursor controls" in the settings menu.

The compass has also gotten an overhaul, which makes it much easier to read now.

Clicking on buttons, such as for starting a new game, will now make a pop-up appear, asking you to confirm your choice. 

Other changes

Many new sounds have been added and old ones have been changed.

The main menu has been completely redesigned.