The build-kernel script was forgotten to commit, it is needed to build the kernel
To make the build-submodules script more readable and extendible i've almost totally rewritten it using functions
the build process is also started in its own subshell, so that we dont need to hold track of the current directory and make error handling/status info easier
The script was originally named `build-docker-subpackages` and executed docker for every package built.
This has now changed so that the user could choose to do a docker or native build.
The readme is aldo updated to reflect this change.
