Remove the need for gzip apk

Today and apk package is built by data.tar.gz, control.tar.gz and signature.tar.gz. Sometime (when using apk in yocto) the speed of build is more important than the size of the packages. Therefore it should be possible to create apk-packages with only data.tar, control.tar and signature.tar. That is no compression. apk should have support for installing apk packages with different compression (including no compression).