Optimize folder structure

Summary

Before releasing v4 we should consider optimizing the folder structure a bit. I propose that we introduce a separation between source code and the duality game engine.

To give a general idea the structure would look like this

root
  Assets (formerly the media folder)
  Source
   Solution.sln
   Launchers
     Gamelauncher
     Gameeditor
   Plugins
     Gameplugin
  Duality
    Data
    Plugins
    rest of the buildoutput....

Duality does use some hardcoded paths so these have to be changed to make this work.

Analysis

• Simply zipping the duality folder would work for distributing the game.
• Easier to find the .sln file
• Easier to ignore certain files with wildcards from source control as files are not mixed together anymore.

EDIT: updated example structure

[Barsonax]

I think for now we should keep DualityLauncher and Editor in the root folder as thats much easier to implement. Moving further discussion about this to #828

[Barsonax]

Decided to go with Import as name and keep it in the root folder