Removed source directory

I removed the source directory, since it makes installing using composer a bit of a headache. Right now, if you were to use the project as it stays, you would have it install either in the vendor directory under a source folder or you would at least have the source directory in your directory, which means you would either have to work with symlinks or point your vhost to the source directory. With this change and the addition of the oxid-shop type to the composer/installers package i made and which will hopefully be merged soon, it should be possible to install your oxid shop, anywhere you want, using the extras->installer-paths directive of your composer.json. Also, having separate folders for source and tests doesnt really make much sense, considering the fact that you need the one to run the other. If you however still feel the desire to keep those separated, you might want to consider to put them in separate composer packages, which can be installed separetly.