Merge different engines into single one

[FolkertVanVerseveld]

Since the project has started, several engines have been written to try out different approaches. As the goals of this project were narrowed down further, it has become apparent that the best approach to make it maintainable for a single person is to use relatively modern technology (i.e. OpenGL without using fancy shaders as AoE does not need flexible stuff, just easy-to-use stuff) and use several libraries that have already accomplished these goals.

• [ ] Purge empires/
• [ ] Purge empiresx/
• [ ] Merge code into new engine
  • [ ] Merge empires/ into new engine
  • [ ] Merge empiresx/ into new engine