Loading indicator

As the game might grow in size especially if more sound and music are added and as most of the content is loaded right away, a loading bar could be useful in the beginning of the game to show that something is actually happening and the game works.

Start by locating the game's startup entry point and how content, sound, and music are loaded. Determine where the initial loading state can be observed; done means a loading bar is visible while startup content is loading and the game proceeds normally afterward.

Written by the indexing model from the issue text.