server: remove being picky about user in start script

Until now the start script would error out if the user calling the
script is neither root nor peerdrive. Instead of handling and
hardcoding that in the script, the caller (e.g. the system specifc
init script) should be doing this right and we should trust him.
server: add foreground option to start script

The OSX daemon manager launchd daemonizes processes himself and thusly
requires all processes to stay in the foreground.
server: add script to install on OSX

This commit adds a script which basically is a stripped down version
of server/install.sh. At some point in the future the scripts should
either be united or the common parts should be seperated out.