Added external depencences previously in separate repo to the portable project.

Before this commit, external depencences such as Openal, SDL, and
SDL_net were in a separate repo and placing along with this project and
renaming folders were mandatory.

Now the project is fully portable. You only have to clone and open
7kaa.sln file. It's set up to VC STUDIO 2012 but cand be easily
downgraded under project properties (Under 'compilation toolset' set the
proper compiler environment for your version [names may change between
versions]).