build script: added support for new command line parameters
--vmram 128
--vram 12
--vmsize 200G
--terminal-only
--no-default-applications
--current-sources
--64bit-linux
--64bit-kfreebsd
--32bit-kfreebsd
--enable-whonix-apt-repository
--whonix-apt-repository-distribution stable
--whonix-apt-repository-distribution testers
--whonix-apt-repository-distribution developers
--minimal-report
--skip-verifiable
--skip-sanity-tests
build script: allow help-steps/parse-cmd to overrule default variables set by help-steps/variables; better support for environment variables