Make the game playable without original files

[Solen1985]

This is going to be a very low priority task. I made a start today by adding the fallback font, which is needed to inform the user that files need to be copied to the data folder. Eventually, I want the game to work without the original game files, by generating very basic placeholder graphics.

[AlexFolland]

If these placeholder graphics are in a common file format, other users could help the project by making free graphics sets, like has been done with Freeciv.