Updating install-spotify.sh and installation package.

Major update. Don't require spec file to be installed, download it instead.
Use set -e instead of home-brewed safe-run. Use rpmdev-setuptree to create
a personal build environment if needed (i. e., so user can build without
root privileges). Only require root privileges to install/uninstall. Use
spotify-make to download .deb packages. Use rpmdev-spectool to download
other sources. Don't hardcode locations to %_srcdir, %_topdir etc.

As a consequence of above, the spec is excluded from the spec file and
the README updated.